deSitter: Check closely - just before the sudden left roll, it seems to me the plane is trying to roll RIGHT, very slight, almost imperceptible - but definitely there. In particular, just before tucking the left wing under, it seemed the right rolls were about to get out of hand so he overcorrected with left roll INPUT, and then snap - too late.
In other words, he's in a fast steep turn with highly modified aerodynamics for his airplane, and it has basically stopped flying normally and is trying to roll right - probably because the outer (right) wing is stalled. It's in a high-speed stall induced by too much speed through a turn.
...or more logically, the result of wake turbulence from the aircraft ahead of him.