Originally Posted by
TEEEJ
Probably the fuel tank exploding? See following footage of Syrian Mi-8 with internal fuel tank visible.
I strongly tend to agree.
I think the trail you see in the video might be fuel. Possibly pouring out of the aft ramp. The explosion pressure wave only seems to be as big as the fiireball, this too me points to a combustible liquid / vapor explosion rather than HE stuff.
Therefore I don't think it was hit a second time by a missile. Also no trail and too big / fiery of an explosion for a MANPAD or RPG..