He marked him??? Already? uhmmm

Probably not?

I don't know what the rules are in this omegaverse, but I am under the impression that you need to mark during a knot to form a bond

I think you're right

Yea, if I'm remembering correctly, the marking he's doing now is just like a pheromones mark so people know he's kinda with someone at the moment but it's not the permanent mate marking when the seme would knot first