They could have jumped into the boat, but the explorer lifted a heavy knotted rope from the floor boards, threatened them with it, and so kept them from attempting the leap. (44)
Although we don't get any description of what he's feeling internally, it seems clear from the explorer's actions that he wants to leave the colony and everything he saw there behind. He's quick to escape, and he doesn't want to take any part of it with him. Something has deeply disturbed him.