I'll relate my experience and thoughts.

I had a GF who set-up an appointment with my old T. After the phone set-up, my T realized it was my GF--we were having problems and she was getting a little strange. In session T told me about "someone making an appt" with her, asking my GF's last name, but without literally saying it was my GF. So she could formally maintain privacy for the person who called her. Anyway, she explained that as a matter of conflict of interest how T's won't meet oftentimes with people who are close or involved in the lives of an existing patient, etc. It was all code for "Your GF made an appt, I now know it was her, and I'm not going to see her." Later that day, the GF came over desperate, angry, and crying b/c my T cancelled with her, playing dumb like she didn't know why--my T just told her there was a conflict of interest. I'd never told the GF my T's name, but easy enough to find out. The GF acted like it was totally random that she made an appt with my T, out of at least 1500+ T's in my 2.5 million+ metro are; claimed someone gave her her name. Lie. I broke up with her shortly--we were on the rocks anyway. Turns out she thought I was having an affair with my T--paranoia--and great, great, great ugliness later ensued with actions she took involving that T and me, successfully (for her intentions) bringing an end to that therapy relationship.

In your case you need to get 2 different things sorted out, the "friend" and the T.

How big of an area do you live in? How likely is it that he'd have without trying chosen your T? In my case, it wasn't believable (for issues beyond merely the stats).

Why did he want to see your T? Did you talk about her? Along the lines of what Sunrise said, it sounds like a way to try to get close to you--maybe he thinks that in talking about you with her he can learn some things.

You have to figure out your T. I can't from your description, just as Sunrise said she seemed to contradict herself.

It sounds like she did what my T did, which was tell me solidly but indirectly without absolutely identifying my GF that my GF was the person in question.

Why see him? Well, you didn't tell her it bothered you clearly enough it seems. I don't think she should've seen him because it seems to bother you enough even though you weren't adamant about it. The area size is a factor; if it's not a very small area he should have plenty of options available.

I think he's up to something weird enough that you shouldn't risk making therapy seem uncomfortable for you. That would be horrendous. You don't have to serve his needs, protect your therapy and let your T know it's too much of a concern for you. If it's bothering you enough to write about it as you have here, it could easily hinder your therapy progress.

It doesn't pass the smell test with this guy, and the potential downside could be tremendously bad for you even if it is innocent on his part and devastating if he is up to no good.