I'm not going to question you, because the plane did indeed have enough energy to the "flip". I'm just going to suggest things about the speed. The approach speed a 777 at 250km/h, is correct, that's 134 kts which is maybe a tad bit slower then what it should be. However, the NTSB confirmed today that the aircraft was significantly slower than that – which why the plane ended up coming up short and stalling. Furthermore there is at least a couple seconds of the plane skidding on the ground which would have slowed it yet even more before it did the "flip".