Could you pretend you're interviewing him, like for Rolling Stone or something?
Casual, human, and not at all "OMG I'm talking to someone famous!" It's just a conversation like you'd have in a waiting room.
Start with, "I admit to feeling a bit awkward. I didn't realize my mother had taken up matchmaking. So how did you meet her?" A little bit vulnerable (but in a way that doesn't harm you), a joke, and a question. Then let him talk and ask follow-up questions if there's a lull. Limit it to 15-20 minutes then check your gut. I bet you'll have more questions after a day or so.
Your mom's kind of cute for doing this. But if it becomes intrusive, be sure to tell her that it's freaking you out and you'd like to meet people the old-fashioned way -- at a bar, at church, or both.