This is the frame the ball hits the ground and as you can see you can not tell if there is a mm of gap between his forearm and ball. Hence BOTD.
For me I would change the rule to:
1. A try can only be scored by the hand forcing downward pressure on the ball with some element of control
2. If you can not be sure give it back to the ref to make a judgement call, no BOTD nonsense.
As I said this should not have been a try but with the current rules it has to be given.