Ostensibly, by "that," you are referring to the spiritual aspects of navigation noted in the article. But the "ole racist European trope" may better be classified as a plain acknowledgement of the facts on the ground. For example, the article states:
"To show that Polynesians descended from Europeans, Abraham Fornander in Hawai‘i, and Edward Tregear and J. Macmillan Brown in New Zealand, built the case at the end of the 19th century using the emerging science of linguistics to trace Polynesian languages back to Sanskrit and to European languages."
and:
"Ethnologist S. Percy Smith was one of several scholars who praised the Polynesians’ “intelligence, their charming personalities, and—one likes to think—their common source with ourselves from the Caucasian branch of humanity."
We could probably look up Fornander, Tregear, and Brown in the literature and gauge their relevance in their field. Ditto for Percy. Maybe it really is a liberal conspiracy to undermine the meritocracy. From the 1930s. Before we do that, though, maybe we should do a search on that tool of the left wing, Google, which turns up https://teara.govt.nz/en/ideas-of-maori-origins/page-2 among the top results for "aryan polynesian theory."
I think the quotes above more lend support to the idea that the article mentions in passing an accounting of the history of the (at least) sometimes racist scholarship in this area, rather than a trope. It's certainly possible that there are "factual tropes," I suppose. Nazis were, after all, pretty bad, no matter how many times we say it. (I have to say that I do think it's cowardly of people to hide behind the connotation of "fiction" in the word "trope." Like, they can't say "lie" or "propaganda" without revealing their racism, so they use "trope." Cheap.) However, calling something a "trope" in order to dismiss it as, I dunno, SJW tears or whatever, is a bit disingenuous. One might even call this common tactic an actual "trope," and a counterfactual one, of the alt-right.