I believe he hated that stp was defined as grunge, but to be more precise - grunge rip-offs. The media was so unfair towards them and I don't think the boys wanted to be "grunge" but just a rock n roll band. Had they released Core maybe just months earlier, the hypocrite media might have chosen some other band to bash...
That definitely makes sense. Considering the music industry wants to be so cookie-cutter and in with what's "hot today," I wouldn't be surprised if they were also somewhat pushed into a grunge-like persona by the record company. I remember reading Scott saying he was offended by being constantly compared to Eddie Vedder, because he considered himself and Vedder to be significantly different, yet the tabloids and critics found nothing but "similarities" between the two.