Just ride your bike and enjoy it. Don't get into this sort of stuff. There's a million reasons why you could pass someone and then they pass you, most of which are benign. If it motivates you to give chase, do it. When I'm riding in the flats of Florida when I visit my parents down there, if I spot someone ahead of me, I might try to catch them just to push a little, but usually I just ride. But don't get into a racing game with people who are probably not racing and don't draft someone unless you tell them you're there and they say OK.