Yes one male rolling another on his back is a dominance thing however, their ears are perked, tails are wagging and they are bouncing and running around, when my pit, shepherd, or wolf get serious they ears go back, tail goes down, hair on the neck gets raised barking goes to snarling and there is no bouncing or running it becomes a straight standoff. I just watch the video for a second time and I don't see any indicators of aggression, they aren't even vocalizing.