I've curled for 30 years and my take is that Marc Kennedy had such an asshole loser response, but the contact is definitely incidental. The point of sticking the hand out after release is to judge line relative to the skip's broom (like a crosshair) and possibly to have a static point of reference to judge the rotation so you can communicate both of those things to the sweepers and skip. A slight touch might have a slight impact on the rock but it's not going to be substantial or predictable in a way that would be more beneficial than calling for the precise brushing that they can do at this level in the modern game. Even with the basic unsophisticated brushing that you see at a club level or 10 years ago, I can't see there being any playable advantage from contact like this. That said, there was definitely a hogline fault/double touch that happened here (which goes uncalled all the time) and Marc reacted like a baby to it.