George is a rare manx monkey.So there you go - the reason he doesn't have a tail like other monkeys.
George is actually a child who is pretending to be a monkey.It would explain why everyone calls him a monkey when he's actually a chimpanzee. A kid wouldn't know the difference, and probably wouldn't know to correct you if you said, "Oh, you're pretending to be a monkey". Also, when chimpanzees mature, they can be very dangerous. If George is actually just a child, it would explain why he's able to run around without ever getting into trouble or taken away by animal services. And any particularly crazy happenings can probably be explained by a particularly overzealous bout of imagining on George's part.