[blam]

"My wild guess is that it's somehow related to the Polynesian expansion. "

This is about the time of the Dark Ages. Remember Mike Baillie (and others) believe the Dark Ages was caused by the earth being hit by a comet/asteroid swarm. The Dark Ages were worldwide.

[SunkenCiv]

David Keys claims that a volcanic eruption is responsible for the "Dark Ages", and Borneo is fairly close to where he claims the eruption took place. Not that I buy that of course. :')