I think this really has to do with what other people think of you the first time they see you. Looks combined with "energy" or something, I don't know the technical psychological jargon.
People seem to subconsciously think of me as a leader, even in situations where I obviously am the newest person on site. I have a way with words and others always think that I am very intelligent. I am not even trying to make others think of me as a leader, they just do it. Of course, this isn't always good for me as other persons in the group sometimes take this as a threat, whether it is the groups real leader or just someone that wants to be the leader.