Observing the video link posted by Carnage Matey, I seems that the plane touched down in a "normal" attitude - how hard I can't judge - but what I see next is:
-the MLG bouncing up a few feet before the NLG even touches the rwy;
-NLG hits the ground with MLG still up pushing it down again;
-After this second MLG touch down, the apparent porpoising effect seems almost controlled, with the plane in a G/A like attitude, but the speed drops in the middle of this second bounce.
-Plane hits the rwy NLG first this time, the A/C bounces again, sits and slides on its tail, wheels off the ground. Without LH or RH wheel lateral support it can tilt either way, gusts, cargo shifting do the rest, flipping it upside-down.