I don't think Ethan was a "real doctor" in the sense that he went to medical school. I believe he was educated on the Island, just like the rest of Othertown. If you believe Ben Linus spent his whole life there, then so too did at least a part of their community. Mind you, I do think the jury is still out on all that! Ben is a lying sack of s***, and thrives on messing with fragile Lostie minds.