This is how much Facebook tracks you.
I once created a fake account with a fake name, a new email address and no phone verification.
I created it on a PC with geolocation disabled and using incognito mode in order to have no previous cookies.
I had no other Facebook accounts at that time, so there was no way for Facebook to know who I am.
However, as soon as I logged in, Facebook suggested my real life friends as friends.
How the hell did it know who my friends were?
Again, everything was fake, geolocation was disabled, there was no browser history, and I didn't have other accounts.
I reflected for a while and realized the only way it could have done it was through WhatsApp.
Basically, my phone with WhatsApp and my PC were connected to the same WiFi network, so their public IP addresses were the same.
That way, Facebook detected it was me simply because I was using WhatsApp with the same IP, even though it was from another device.
Pretty scary stuff if you ask me.