Personally, I'd avoid any social networking with a T or pdoc. Fortunately, my T has a very open policy on social networking - he doesn't do it, at all. He mentions this on his website and he mentioned it when I first met him.

I saw that as a "hard boundary" and respect it, but I also like it. To me, T is so intimately private and it's SUCH a small world, I can't even begin to THINK "what if one of my friends goes to my T", or what if someone from LinkedIn or Facebook recognizes his name and knows I'm associated with my T.

I would ignore the connection and even maybe mention it to your pdoc that you don't want to engage in social networking with him for privacy concerns.

As for how he found you, it most likely is from his email list, or yours and his profiles, if you share the same town, etc. I remember when I first started on facebook, I was getting "who you knows" from people I haven't emailed/talked to in 10 years! LOL Talk about weird.