They must have missed Swedish. We don't have 'huh', we have 'va'.
I also read in the source: "Therefore we collected data from recordings of naturally occurring informal conversations in a sample of 10 languages from 5 continents, varying fundamentally in terms of phonology, word structure, and grammar (languages 1–10 in Figure 1)". That sounds pretty far from "all languages" as in the title.
I don't think the point is that it would sound like "huh" in all languages, but rather that there is a word used like "huh" in all languages. "Va" definitely fits, as you even said "we have 'va'", proving the point of the article.