I remember that. After the Mulwala tornado, which was actually later upgraded to an EF4, I remember thinking there was no way they could call it "mini" but they did anyway. Needless to say, there is nothing remotely "mini" about a violent, multiple-vortex EF4 tornado. IDK why they insist on doing that. Do many Australians believe that tornadoes are a strictly American phenomenon, and assume any tornadic event in Australia is not a "full fledged" tornado because of this? It's bizarre to me.
The rating of the Mulwala tornado is a bit more complex than that (I was pleased to see it got a mention in this thread BTW). It's officially recorded as an F3 on the Bureau of Meteorology database (which is absolutely horrendous and includes no other information), and the Tamleaugh-Swanpool tornado from the same day, which tracked about 60 km, an F1. The most intense damage I damage photograph I saw (but didn't save and it's over five years since I saw it) was low-end F3 - a two story house had the entire upper story removed. It's worth pointing out that at least since the 90s or so Australian building standards are much higher than the US average, because though there is some variation with likelihood of certain threats, we share our standards with earthquake-prone New Zealand.
The EF4 rating (and EF3 for the Tamleaugh tornado) was applied by the BoM meteorologist Coombs, whose presentation you might have seen. That rating appears to be inferred rather than derived directly from DIs, as there were almost no DIs other than trees on the stronger (left) side of the path, or in general really. This is supported by tree damage and a 335 km/h reading from the Yarrawonga radar, which the tornado passed very close to. So far as I know it caused no actual EF4 building damage. Tree damage itself is also a bit more difficult as many Eucalypts shed thin outer bark (that fuels our famous bushfires) and it's hard tell if this or live bark was removed. That rating is very liberal and would never pass in the US, although as we have a thread complaining about, some recent ratings there are ridiculous low-balls (I'm convinced if April 27 was rated the way it's been done recently we'd only end up with 2-3 EF5s, they wouldn't upgrade Rainsville and the ground damage at Philadelphia isn't a standard DI, they seem to be less inclined to call a spade a spade now). The most disappointing thing is that a formal paper was never published on it.
There is an Australian researcher currently at Central Michigan University, John T. Allen, who has done some work on Australian tornado climatology - he was actually intending to publish in 2016 but still hasn't got around to it, and has a paper on tornadoes in 2013 going to press in the MWR soon. He gave the Mulwala storm an F3 rating. Ratings in Australia are very ad-hoc and it's only been recently they've been done officially and formally at all. We officially use the F scale and not the EF scale. This lead to some silly situations, like a 2016 outbreak in the Southern Flinders ranges, where they used the EF DIs and 'converted' them back to F-scale windspeed. There is only one definite violent tornado in the database, the Bucca Queensland F4 on 29/11/1997, but as far as I know even that is not 'official' as such and is based off reports similar to the pre-1971 F-scale ratings. Unfortunately the original report is unobtainium and though I have some photographs of the tornado I have never seen one of the damage.
So far as people's attitude to them here, while with the internet there is less of a perception that they don't happen at all, they certainly aren't put on the same level. Most of our tornadoes here are very small and short lived, and often lack the full condensation funnel that makes a tornado look 'tornadoey'. Bigger ones are very rare and even more rarely caught on camera. The Mulwala event was by far the most significant for at least 21 years. And it's led a 'tornado = mini tornado' mindset. In the South fire and drought dominate all other weather worries.
Australia's climate is not very good for tornadoes, especially big ones. While there was a period where it was thought we might get 2-300 a year at a time when the US was thought to get about 6-800, we now know it's more like 20-30 at the most (the last few years have been very barren, with only a few reports, and the severe storm seasons have been bad in general), though Allen thanks it may be closer to 50. Far from being 'second after the US/Canada' as was once sometimes asserted, conditions are less favourable than the Rio de Plata region, Bengal, Europe, China and probably a few other places as well.
The basic issues is we are too dry, too far north and have the wrong terrain. As a result it is very rare to get the required combination of moisture, instability, shear and helicity to produce strong to violent tornadoes. Usually one or more is missing. Moisture is the biggest, because the synoptic scale systems advect over desert dew points over 15°C aren't common outside of tropical-influenced areas. This leads to weak, high-based storms. Also hard to get an EML when there's a hot desert near sea level directly upwind - the USA's terrain is much better arranged.
Shear is quite hard too, moister troughs are often weak and slow moving, low shear and produce intense rainfall instead. Meanwhile the strongest low level shear is usually with cold fronts that have boundary parallel flow and little helicity.
Tornadic supercells associated with large scale systems that produce the classic east-southeast tracks aren't that common and occur in a scattered area especially on the windward side of the Great Dividing Range and the plains in Central-West NSW etc. Coastal supercells tend towards hail/rain. Those in SE Queensland are quite different, associated with somewhat smaller troughs. These tend bud off the NSW/QLD Border Ranges and move NE and are usually HP cells with big hail - there have been some very destructive hailstorms recently. Storm modes in general tend towards HP or just generally messy, when supercells occur at all. There is a much higher proportion of cool season tornadoes, probably about half although conditions are expected to become less favourable. These are usually generated by low-topped supercells (as low as 8 km) embedded in or ahead of cold fronts. Western Australia and Victoria are the most common places for these.
Overall there simply aren't the conditions to get big tornado outbreaks. The best analogy to the big outbreak producing days like those in the US is probably our big bushfire 'blow up' days in Victoria and SE NSW like 16/2/1983 or 7/2/2009. These are prefrontal trough driven and have strong low level shear with the air coming directly off the central deserts, humidity under 10% and sea level equivalent temps over 40°C. The surface based mixed layer on the dry adiabat can be 4-5 km deep, if you chopped the bottom off and replaced it with humid air it'd resemble your US tornado setup. Helicity can be very high close to the trough as well - I once saw a picture of the Churchill fire from 7/2/2009 (when fires killed 173 people) where the smoke plume was bent nearly 90°. This is where you get the big fire events where single fires burn 25,000 hectares or more in a few hours.