I'm heading to Detroit on Saturday and have been up there before and i know the areas you are talking about. From the way you described things you were fine with your actions. As someone else posted, i wouldn't have my door open and the keys are always in my pocket. In a similar situation, i would have maybe drawn as he rounded the front of the car, not waited until he was at the door. He could take one leap from 5 feet and be on you before you could react in a defensive way. Plus the fact that you haven't heard anything from them, you should probably not worry. The police would have contacted you by now if it was an issue.
Oh, and get a new GPS if the one you have got you lost