Facebook has tons of info on people who never made an account on it, it's called shadow profile and it's all thanks to stupid friends.
FB collects phone numbers from phones of people who download their shitty apps and cross-references them with their database of phone numbers. Phil has a number 123-456 in his phone address book assigned to Frank Walcott. Mary has number 123-456 in her phone address book assigned to Frank Walcott.
Also, Phil and Mary have each other's phone numbers, so FB can with 99.99% certainty know Frank Walcott's phone number, even though the guy might have never made an FB account and thinks he's safe and anonymous. The same process can be applied to names of WiFi networks, for example. In fact, just having the ability to know the names of available WiFi addresses precisely pinpoints the user geographically.
FB collects so much data, it boggles the mind. Downloading any of their apps is like putting the phone through a data juicer, it just collects everything.