It is laughable to think that the first supported travel over water was done in “boats“ or by “sailing“. Children instinctively climb onto floating objects. It seems very likely to be that some unwary homo-something crossed an unswimmable span of water quite by accident and survived. Perhaps some other individual observed their fate and followed, perhaps from the same species or perhaps not. Perhaps alone, or perhaps with others.

The evidence is merely that there are early tools on islands.