One explanation is that Facebook collects its users contact lists. That way, it can create 'shadow-accounts' for people that don't have yet a Facebook account.

One explanation is that Facebook collects its users contact lists. That way, it can create 'shadow-accounts' for people that don't have yet a Facebook account. So when/if that person finally creates a Facebook account with some data tying him/her to a shadow-account, Facebook can directly propose relevant contacts and already knows a lot about that person, including his/her real name.