[woliveirajr]

> Facebook and the other companies in the Facebook family also may use information from us to improve your experiences within their services such as making product suggestions (for example, of friends or connections, or of interesting content) and showing relevant offers and ads. [whatsaap privacy policy]

Many possibilities here:

1 - whatsapp connection with messages exchanged

2 - contact list loaded by whatsapp

3 - psychiatrist secretary number in whatsapp

4 - friends in common

5 - places in common

[dev_256]

Or 10 people checked psychiatrist’s facebook profile, facebook found common interest, saw that none of these people are fb friends and suggested to become friends, because hey, you all have something in common, you are all interested in this person.

[raverbashing]

Yes, I believe this is what happened

Fb will suggest you know person X if a) you looked at person X's profile or b) person X looked at your profile