I'm not watching it again but there is a good 2-3 seconds where he's content to watch the 5 on 4 play unfolding in front of the net, and when he decides to get back in doesn't have much issue getting back up until Garland tackles him again.so when he's trying to get up and punches Garland in the back of the head because Garland is holding his arm...was what? all for show? That's really weak reasoning.
What's most relevant though is what the refs see. When you get your replay view can hit pause and start analyzing the pixels it looks like his arm is in Garland, though it's pretty subjective to what extent that's hindering him. From the refs perspective though they probably see McDavid take down Garland then contently sit on him for a good stretch. Right after Bouchard decided to sit on Pettersson at the other end of the rink giving Edmonton an advantageous 5 on 4 going back in the offensive zone.
If the refs were going to make the 'right' calls, the McDavid/Garland mixup wouldn't have happened because they would have called Bouchard. Personally watching it real time I was laughing when Garland started grappling McDavid because I knew after the two take downs they let go they were going to keep letting em play and weren't going to call this either. Up until the point McDavid throws a little fit.