I think you will see it on youtube if you look it up but there was intent there to attack the ball. You can’t see whiteheads face but he definitely can see where the ball is and Intentionally puts his hands on the ball. He pulls at the ball downwards and then comes free. I’m not a Ref and will go with your judgement but in my own opinion he definitely intends to strip the ball as opposed to tackling him.
I am not sure if he intended to strip the ball. Either way as it was one on one a strip it is legal. The only way it is not a knock on is if Whitehead propelled it towards his own line. His action would lead to the ball being pulled towards the Tongan line and a knock on by him. The fact it went towards the England line would suggest Fafita propelled it in that direction.