I think you handled it well--brief and polite.
I don't know the details of your relationship, but it's been my observation (in my own life and the lives of others) that when exes want to come around, it's usually because they want to manipulate you. Some people think that if they "throw you a bone" every now and then, they will keep you interested *just in case* they ever decide they want you back. It's not right, and I admit that I've been on both sides of this coin.
