How does facebook know I'm not really Dean Winchester?

[Kellin Quinn]

Basically I was bored and being a fan of supernatural i decided to make a facebook account for Dean from it (not a page, a personal account). I typed in the details and used the same email address as my actual facebook account and it said i already had an account, so i changed the email address to my other email and still it wouldn't let me create an account. It said: We require everyone to use their real name on Facebook. Learn more. I clicked Learn more and my name followed all of the guidelines so why didn't it work? It still didn't work when i changed Dean to Sam. Does facebook know that Dean Winchester is a character?
Thanks for the answers everyone, they all helped me out equally i can't pick a best one