I think you are taking it too personally. And like misty I think it's rude to mention it.

One of the most important things you need to do as they grow is stay out of their friendships. Don't fight fires for them and don't take things like birthday parties too seriously. Assuming the worst doesn't help you or your child. And saying something is a huge social no no and could make things very uncomfortable. Let it go and continue to allow your child to choose his friends. I promise you in the grand scheme of things it's a blip on your child's radar. Nothing more.