What I'm saying is they often actually mean "country", but that is less fancy sounding. A nation-state is just one specific type of polity, certainly not the only type which organize attacks.
You’re overthinking it. “Country” is simply more ambiguous when used as an adjective. “F5 announces attack from country hackers” sounds silly and confusing.
"F5 announces hack by foreign country" (or the infinite variations of) is less silly than "F5 announces attack from nation-state hackers", you're just used to hearing the latter repeated every incident. Anyone can intentionally use a phrase poorly, pointing out a silly sounding phrasing exists adds nothing.
Not that "F5 announces attack by state sponsored hackers", "F5 announces attack by nation-state backed hackers", or "F5 announces attack from nationally backed hackers" have to be invalid, particularly since the latter is often what is actually most specifically correct anyways.