I agree with @Dolphin2010, he could be given a yellow for a pointless attempt at swinging his arm after the hit, but even that would be harsh. At least it only cost his team a few minutes with a man disadvantage. He will not be given any ban, you can be sure of that.
I think he has his Knock On interpretation technically correct, but he seems to be over zealous in attempting to correct everyone else's interpretation. He needs to remember too that a ball passed/lost backwards OR FLAT is perfectly ok. I always love his refereeing as he allows play to flow, leading to some of recent years' best games, so why be so picky with the knock ons...?