Yes it's normal behavior. No, you don't have to be more aggressive. Just ride smart. One of the dumbest riders on the Nyack Ride I've been doing for 20 years is one of the fastest, a Cat 1. He is however utterly skullfarked. He'll try to move up between me and the curb when there is barely enough room for him to squeeze through, @ 30mph, for no apparent reason. He may be fast, but he is a moron. Intelligence level is not linked to bicycle racing ability. Some of the fastest guys are among the dumbest.

So use your common sense, don't ride stupid, and stay away from the morons that do, whether they are a Cat 5 or a pro.