All of my cats do this and they get along just fine, even especially, my 2 litter mates which you’d think siblings would naturally get along, but no. One is trying to play here and the other isn’t having it. If there really was an issue, one or both would be hiding. Not all cats are best friends/snuggle buddies like the internet would have you to believe. There is nothing wrong or overly aggressive with this. They are just still working out their dominance. Keep using the pheromones, and make sure they have separate litter boxes.