While officers can make contact and engage in "small talk" ("fish for information" as one poster put it), I see nothing that indicates that the officer developed further information which would have warranted extending the contact with the OP. (Granting the fact that I have only seen one side of the story.) It's very hard to make a case for reasonable suspicion, based on clearly articulable facts, when the articulable facts all consist of activities that are entirely legal.
A gunfight is not the time to learn new skills.
If you ever have a real need for more than a couple of magazines, your problem is not a shortage of magazines. It's a shortage of people on your side of the argument. -- Art Eatman