Are you sure they didn't do something to get pulled over? Or have you gotten in trouble with your local cops enough that they would pull it over just to see what you were up to... Just curious, sounds like we didn't get the whole story, did you?
certain officers will find reasons to pull people over, but that's not a valid one. If the officer knows who the car belongs to, and pulled that car over because someone else was driving it, I think that would be either called stalking or over-protectiveness.
That would be pretty creepy if they knew me and my car so well they would know someone else is driving it. I prefer to remain beneath the radar of the coercive arm of our civil government. But if somehow I had allowed the cops to know me that well, they could always say they wanted to make sure the car wasn't stolen.