Agreed. One has to remember that it looks like this was a tract home (aka cookie cutter home). If there's one type of permanent house in the US that can be well-anchored, but still be slabbed by tornado below the violent threshold, it would be tract homes. The problem is that these types of houses tend to be structurally weak, regardless of how thoroughly they are bolted down.
The comparison I always make is that it's like bolting down a cardboard box. Doesn't matter how many bolts you install if the structure itself is frail. Not saying this wasn't an EF4 though.