This Polynesian contact is a genuinely separate event from whatever produced the Population Y signal.

The Population Y signal involves allele sharing between South American populations and Australasian populations — specifically Australia, New Guinea, and the Andaman Islands — not Polynesia.

Polynesian populations are genetically distinct from Australian and Melanesian populations in ways that matter for this analysis.

The ancestors of Polynesians moved through Melanesia and mixed with Austronesian populations before spreading across the Pacific; the Polynesian genetic profile is a specific combination of East Asian, Austronesian, and Melanesian-related ancestry that is different from the purely Australasian-related ancestry that the Population Y signal is most similar to.

The Polynesian contact is sometimes raised in discussions of Population Y as if it might explain the signal, but the two phenomena involve different populations, different time periods, different geographic patterns, and different statistical signals.