Yes "twisted wrench" that's what I'm also thinking as a possibility .... I have had an uncontroled ditching once, and on impact, engines didn't immediatly stop by themselves, and instead stabilised at an intermediate regime, but the "flexible couplings" linking their power shafts to the gear box, broke .... we can imagine that this condition may, as well, have caused a sudden uncontained overspeed. Or else,as you say, the forces of impact, caused a displacement of the power turbine out of its shield while the engine was still running.
Once again, just pilots sharing ideas ! Investigators probably already have a clearer picture now.