Shor had been aboard the boat previously. Much like those who now entered, he had been asked aboard by the Ancient Goat. His first instinct, of course, had been to bash the goat's brains in, shattering his skull, and then perhaps slaughtering the crew. However, the goat had then repeated his request with quite a lot more diplomacy, convincing Shor that he meant no disrespect, and was not treating Shor as a slave. It was a request, not an order. While Shor didn't see the difference, he was smart enough to know he was dumb, so he'd just gotten on board.