This why you run a blow proof bell housing and scattershield

I saw these photos yesterday. My guess is that flexplate is not a heavy duty SFI approved piece. Maybe it tore away from the crank flange first, starting a massive vibration that broke apart the case, then allowing the converter to come out. It's amazing how much damage occurs when something rotating with a lot of weight decides it has had enough.
I hope that dude is ok.