I agree that the defender initiated contact--contact he was entitled to make, as the offensive player had the ball. But just before the shot, I see the defender's body move away from the offensive player towards the goal. It's not violent, and his head does not snap, but the only way that happens is if the offensive player pushed him away with the off hand. And he's not entitled to do that.
I don't think that is the only way it happens. When a small person is latched onto a big person, and the big person turns hard and then stops, the small person often keeps moving, creating space. The defender was moving himself in that direction as well, attempting to get in front and not be turned. There was no obvious use of the head or arms to create separation, at least not from the view of the camera. So no contra was called.