The techniques in this article would be considered common knowledge for any of the prerequisite classes you'd need to take to be able to follow a course on Higher order Fourier analysis.
I wouldn't say they're unrelated, but if you want to know whether both uses of the phrase "higher order" have any relation then no.
I wouldn't say they're unrelated, but if you want to know whether both uses of the phrase "higher order" have any relation then no.