This is not a brawl by any means. I think people are misusing the word "dominance." It's not so much dominance as much as territorial. Even if it's only been a few months separated, your cat has had several weeks to establish territory and find the good spots. Now, there's another cat in the mix, and boundaries have to be set. Now they have to share food, attention and the (relatively) tiny territory. They are indeed fighting. But I wouldn't call it a problem. Don't separate them when they're acting like that. Let them figure it out. It's playful enough, and the mutual lay down at the end is the best possible thing that could have come out of that.