There were a lot of reports like these that were complete assumption based on the fact that one witness said the airplane had flipped over. It actually hadn't.
I don't think airframes have quite the strength to flip end over end from contact with the ground, even at landing speeds. I can grab this pen rom my desk and throw it on the carpet so it flips vertically end over end. A 777 airframe might do something halfway between that and crumbling as it bounces.