Kangaroo looked like he was trying to befriend the dog in the first one, and the dog looked kinda cool with it.
The kangaroo also looked a little incredulous when he got popped, kinda like, "What the hell are you popping me for!"
It looked like a friendly embrace but watch when the Roo let's go of the dog he tries to kick him.
I read the explanation given in that piece you linked but i think I have a better one...
The roos try grab the opponents head and neck with its claws so that it can't escape the incoming front kick. While it was doing that it found itself having the dog in a headlock. Both of them stooped fighting and froze when the guy arrived making it look like they were playing. But they weren't.
I agree that the roo would of only attacked cos it found itself within striking range of the dog, otherwise it would of fled
Ever had a kangaroo steak. Hmmm beautiful