Boats, obviously. But the settlers themselves were dead. Their descendants may have had oral traditions about how their ancestors reached the island but I don't think we have any evidence that they constituted a seafaring civilization. Those weren't really possible until the invention of reliable navigational instruments such as the compass.

The first settlers got there by a boat thrown off-course by a hurricane, the the seafaring skill was lost, so communication became impossible.

Fair enough.

That's not really relevant to the analogy.