Did I do the right thing in approaching a friend amicably about issues he may have?

It is too late to question it now as you have already done it. You should be able to express your differences and just accept each other for who they are. I would have probably said something else more along the lines of, Hey, I have noticed that you seem to be distancing yourself lately and I am worried about you, and go from there. I would have put it as more of a concern for his well-being from knowing what he use to be like to now.