You are located in Boston, but I assume that this is a smaller town local cop. Either you look like a stoner (and the guy is bored) or someone dropped your name. Another possibility is if you've had ANY type of encounter with LE in the recent past.

Either way, be careful, as they will find a burned out tail light to harass you. Just don't have any quantity on you for a while, and nothing in public. Be cool and keep your eyes open. It will probably blow over.