[pjc50]

I didn't know about this either, but it sounds like you may have found another possible source of the leak: patients putting the name of the psychiatrist into FB search.

If B searches for A and C searches for A, does that imply a relationship between B and C? Especially if they live nearby? Who knows :(

[codingmyway]

In this case I'd almost certainly guess that it is through the phone number. LinkedIn is particularly creepy for this.