This. The user does not have to use Facebook at all, ever, for Facebook to establish the link. If the surgeon has the user's email address in his (the surgeon's

This. The user does not have to use Facebook at all, ever, for Facebook to establish the link. If the surgeon has the user's email address in his (the surgeon's) address book, and he (the surgeon) allows Facebook to access his address book, that is sufficient to establish the link. In the other thread about the psychiatrist, you can find where I discussed a similar incident that occurred some time ago between myself and a professor. Facebook says they don't use location data for friend recommendations (anymore), and given the contact linking it seems reasonable to assume that it is correct.