I think a lot of new American rock bands in the early 90's kind of ended up with the grunge label whether they wanted it or not.
I don't think STP, Pearl Jam or Soundgarden were really grunge bands. They were excellent rock bands from America with a bit of an alternative sound. I always think of grunge as bands like Melvins, Mudhoney, Tad and early, pre Nevermind Nirvana.
Disclaimer: This is just my opinion and not scientifically proven fact. I accept that it may be wrong.