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... ).
Most likely it was originally Quechua, see Adelaar 1998. “The Name of the Sweet Potato: A Case of Pre-Conquest Contact between South America and the Pacific.” https://doi.org/10.1515/9783110806946.403