Some New Zealand ancient DNA experts have concerns about the analysis:
“So, the data that the whole argument is based upon is DNA from one sample that was produced without using standard ancient DNA protocols and analysed without using standard ancient DNA authentication methods. The data presented, to an ancient DNA researcher, ring alarm bells and appear very much like damaged and/or contaminated DNA."
This sounds like a credible alternative to me:
> Dr. Kistler argued that it was still possible that Pacific Islanders voyaged to South America and returned with the sweet potato.
> A thousand years ago, they might have encountered many sweet potato varieties on the continent. When Europeans arrived in the 1500s, they likely wiped out much of the crop’s genetic diversity.
> As a result, Dr. Kistler said, the surviving sweet potatoes of the Pacific only seem distantly related to the ones in the Americas. If the scientists had done the same study in 1500, Pacific sweet potatoes would have fit right in with other South American varieties.
I remember an issue of National Geographic that had a photo montage of about 40 different kinds of potatoes that are still being cultivated in the Andes today. They didn't have any sweet potatoes(1) but I can imagine that in 1500 there were as many different sweet potato variants being cultivated in various places in the new world.
(1) Sweet potatoes are not a variety of potato, so this isn't surprising.
The linguistic similarity they mention at the end is actually even closer: in Maori (and New Zealand English), the word is "kumara".
However, there seems to be some doubt as to whether the word was historically in Quechua, or whether it was introduced later, based on a Polynesian word (e.g. https://anthrosource.onlinelibrary.wiley.com/doi/pdf/10.1525...).
kuumala/kumara: in Tonga where kumala is the word used, the locals don’t know how old the word is. Same goes for their use of “delfin” for dolphin, a creature they have surely known since long before European presence. So I bet the kumala name is a recent loan word. They may have had another word in the past now forgotten.
There's also item?id=16825800, but this looks like the more substantive article.
A lot more theories:
don't they float?