I think that's what the commentators were getting at. He doesn't know how to tackle in union. He's too used to shoulder charges. Tackling in league is different to union not only because of the different rules about wrapping your arms but also because there's no ruck to worry about for the attacker and the defender so you don't need to think about your support and what effect your interaction will have on them.
Probably the most banal couple of non-events that I've ever seen. People seem desperate not to admit that Burgess was hyped up far too much and will never be able to live up to the expectations that people have of him. Making a highlights video of him pushing someone into touch and messing up a tackle is the proof.
Bloody idiot. Kicking at a loose ball is one thing but swinging your big hoof at someone who still has the ball in his arms at the bottom of a ruck is just stupid and dangerous. I suppose he feels like he has to take risks to make an impact considering that he doesn't get much game time, but that's just not on.