Ask HN: FB suggests friends after visiting same city, don't use FB phone. How?

I moved recently to this city (4 months ago). I don't have the FB app or use FB on my phone, don't have this city set as my location in my FB profile and didn't check-in into a location on FB. I never allowed FB on my laptop's browser location access. I followed a page from a local comdy club, though.

Other than that, I have WhatsApp and the Oculus app on my phone a. I have an iPhone.

Any ideas how they know that we have been geographically close? Is it possible they use WhatsApp's location info to match this? I have given WhatsApp location access while using the app.

You have a Facebook account, if you don’t check it on your phone presumably you do on your notebook or desktop. You probably browse the internet at home from the same WiFi network with both your computer and phone. Different cookies from the same IP address would indicate the same household. It wouldn’t take a lot more to know they belong to the same person. IP addresses can strongly correlate with a geographic area.

Since nearly every website has those social media buttons Facebook can track you from site to site even if you’re not logged in.

For sure Facebook knows where you live and has matched up your facebook-free phone to your Facebook account.

I’ve got no experience with actually doing any of this, it’s just what seems obvious to me. I’m sure the whole truth of it is much scarier.

I haven’t had a Facebook account in over a decade but my current girlfriend had my ex-girlfriend from 15 years ago pop up in her recommended list. We live about 10,000 km apart.

If there are any Facebook engineers reading this I must salute you. Your work is amazing.

It was WhatsApp.