I vote for an accident, things happen fast and sometimes people dont realize what they are doing, plus it just doesnt seem possible for a mechanical failure like that. I was at the dealership yesterday to talk to my service guy about it and even let him read your story, he seemed fairly sure that the car could not do that, plus my uncle is a transmission tech for a GMC dealer and he said it is impossible for a car to do that, he also said that the tech who told you about "the torque" opening obviously has never really seen a transmission because there is no such part. Plus he told me the transmission has absolutely no way of changing the engine rpm.