Because if Hutsuls are Ukrainians, then by the same logic, Ukrainians are Russians. The Wikipedia article is just another example of the enforced Ukrainianization of the Rusyn peoples, the same thing the Ukies complain the Russians did to them.
I live in Quebec. Fifty years ago, the descendants of the immigrants from France would have self-identified as "Canadie
ns" (hence the hockey team). Today, they call themselves "Quebecois". Their cousins, who live across the border in Ontario or New Brunswick today do not self-identify as "Quebecois". Yet they are obviously of the same people (and cheer for the same hockey team).
My great-grandfather self-identified as a "Rusyn", but his
children identified as "Ukrainians". One would be hard-pressed to find a Hutsul today who did not self-identify as "Ukrainian".
If I called Warhol, who did not so self-identify a "Ukrainian", I could understand an objection, but the use of "Rusyn" to descibe the film instead of "Hutsul" or "Ukrainian" seems provocative to me.