How did this person get into my facebook account?

I just logged into facebook, and they said there was unusual activity. Someone from Mexico City had logged into my account. I changed my password. How did this person get into my account? I got this really weird friend request from this guy in India that I don't know saying my hair was like a waterfall and my eyes were like bird's nests lol wtf. His picture was really weird too, it definitely wasn't legit. I rejected and reported it, but could this have anything to do with it?