I watched it several times starting about 1:18.. very clear that the tree is faced perpendicular to the bore cut, which is the start of the back cut.. The faller is trying to lay the tree perpendicular to the bore.. There are two smaller trees to the right of the big one, that have already been cut, but are hung up in the vines, and pulling heavily to side-weight the tree. It is that sideweight that caused the tree to fail, well before the back cut was even close to finished.. This is one situation where a little stump shot causes saw snatch.. a level back cut or even slightly below, would have left the saw in the operator's hands, though the bar might have been bent..
The faller never looked up once, and the trainer (if that's what he is) only gives a quick glance up as the tree just begins to move and another quick glance up as the tops are nearly all down.. Could have been nasty...