Facebook recommends patients with a psychiatrist's number on phone friend one another—outing them to each other. 

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Yeah I think he has my number. I wondered about the geolocation too. And there was this rumour about mics on Messenger.
Was it a local rumor? These rumors can be very damaging to security behavior; people make irrational choices with incomplete info.
Could he and you have a common third party in your phones' contact lists? That's how this works, no?
I would guess it was created by an engineer and then nixed by marketing/legal. https://techcrunch.com/2016/06/28/facebook-says-its-not-making-friend-suggestions-based-on-your-location-after-all/ …
I believe they do. I use the mobile site, and got recommended to someone who lives nearby.
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