It's not necessarily "aggressive" in and of itself but it is a show of dominance which can lead to aggressive behavior if not nipped in the bud. Many people mistake that particular dance for a "love" dance or "romance" because they see roosters doing it to hens just before mating, but it is not. Roosters will also do it to another rooster if he's challenging him and trying to establish dominance, mostly commonly when meeting a new rooster for the first time, but can also happen between two roos that have grown up together. It in no way shape or form is meant to display love or romance, it's a communicator of dominance and dominance only. You did the right thing by immediately chasing him off. If you had not or even worse had moved away from him he would have interpreted that to mean you accepted his dominance.