That is a bit petty
Why is that any of your business? That's not much of a friend if you can't trust him.
Unless it's going to affect you personally just let it go. I knew a woman who lied to me about having a terminal illness with limited time to live back in 1999. She's still alive, like a cockroach. Some people are chronic liars, your job is not to unveil them, they'll get tangled up in their own lies.
Why would you doubt him? I think it would be difficult to confirm unless you know the full name and preferably the year he graduated.