[ams6110]

I question point 2. Are you suggesting that Facebook reads my email? Have I given them my email password? If not, how? (I ask, because I don't use Facebook).

Sure, if we have each other's email addresses in our contact lists on Facebook, I can see how the connection was made.

[patcheudor]

In this scenario you don't know if the doctor uploaded their contacts list to FB. You further don't know if they are using a lousy e-mail app that sends usage information to FB, perhaps as part of an advertising integration.