Sounds like WhatsApp and/or your phone number connecting the dots.
Ask HN: FB suggests friends after visiting same city, don't use FB phone. How?
11–20 of 29 posts
Re: Ask HN: FB suggests friends after visiting same city, don't use FB phone. How?
#12I think even your cell phone location data by IMEI is available for sale these days.
Re: Ask HN: FB suggests friends after visiting same city, don't use FB phone. How?
#13Local comedy club plus shared friends.
Re: Ask HN: FB suggests friends after visiting same city, don't use FB phone. How?
#14It’s really impossible to know without more info, as people have mentioned you can download your fb info for some clues. One possibility I haven’t seen mentioned is they are using your credit card data that they’ve purchased.
Re: Ask HN: FB suggests friends after visiting same city, don't use FB phone. How?
#15You visit a website and if they have fb pixels/tracking, it is very easy. FB is everywhere, EVERYWHERE.
uBlock Origin is pretty effective for that issue: https://addons.mozilla.org/en-US/firefox/addon/ublock-origin...
Re: Ask HN: FB suggests friends after visiting same city, don't use FB phone. How?
#16You are missing the most obvious and most likely reason for matching with new coworkers. Your new coworkers searched and viewed your profile on Facebook after meeting you. This is a key way Facebook suggests friends.
Re: Ask HN: FB suggests friends after visiting same city, don't use FB phone. How?
#17FB could buy your data from other networks, provided via some other app.
Also your coworkers probably looked at your FB profile.
Re: Ask HN: FB suggests friends after visiting same city, don't use FB phone. How?
#18Re: Ask HN: FB suggests friends after visiting same city, don't use FB phone. How?
#19Voice recognition, cameras always on and recognizing, could be a million things.
Re: Ask HN: FB suggests friends after visiting same city, don't use FB phone. How?
#20My guess is phone number matching. Your friends use Facebook on their phone and added your contact information recently. That’s enough for Facebook to figure out that it’s a potential match, given that you already have some friends in common.