I think that skeleton is just the skeleton of a dead person, and it is harmless; it's not like one of the re-animated skeletons that you treat like a monster. If I'm not mistaken, if you take the guided tour of Durlag's Tower, the skeleton is merely a prop that the tour guide refers to when he tells the story of the tower. It's kind of weird to think that we expect every skeleton we see to be "alive".
