That damage could have been caused by Converter "ballooning", basicly, this is when the Torque Converter can expand too much under load, the constant expansion and contracting over time, can lead to fractures on the flex plate, the end result (and the first you know about it) is this sort of catastrophic faliure, Crankshaft Thrust Bearings can also be damaged by the same problem.

And as the others suggest, best advice will be from "Auto" experts, not just mechanics