No joke, he has one arm free. He didn't have both arms pinned. Having one arm free has got to give a better chance of breaking fall than none. It was such a fast tackle that he either didn't have time or was too focussed on trying to get a boot to the ball and using that arm for balance. Its quite feasible that a perfectly legal, very fast tackle, where tacklee has both arms free could still strike head on turf, so the fact that a player hits head on turf because of a tackle does not mean the tackle was illegal
It was a very well executed fast tackle and granted it was brutal, but this does not in itself make it illegal. Any time a tackle takes a player to the ground there is a possibility of the head hitting the turf. Are we to ban tackles that take player to the ground?
I emphasised the fact that ti was a fast tackle, because it was one single action. It wasn't a case of tie up player, pause, then drive him into the turf.