They came from a water world being boiled by its sun thousands of years ago.
They used ironified wood to survive the rigors of open space, and hydrogen for fusion.
They used bamboo to build a life raft to cross the infinite ocean of stars.
Somehow they dropped a bunch of seeds over China, probably because they were bored shitless and partying after the discovery of a habitable planet with large oceans.
Of course, the pilot got blasted, and they managed to crash on Rapanui. They erected monuments for those who didn't survive, of course. Then they embedded the dead in their own monuments, as was their custom. All it would take is a quick X-ray of a few Moai to verify my tale, but who has an X-ray machine that big?