> Yeah, the psychiatrist seems the easiest to explain since when choosing a medical professional people may ask their friends who they recommend.

IIRC, connections like those were often explainable by addressbook data. Please assumed Facebook didn't have access to that when it actually did (I'm pretty careful about this kind of stuff and found mine had been slurped at some point, for instance). It's not inconceivable that a psychiatrist and patient may have exchanged emails or phone numbers.