He is the typical "lone wolf" acting on his own initiative, not organized by any particular group. When some "lone wolf" claims to be acting for ISIS without ISIS actually providing any material help, there are usually protests that that isn't terrorism.

He is more like  Elliot Rogers, or Marc Lépine, acting out their misogynistic frustrations, and those were not described as terrorists, either, although there is an anti-feminist movement applauding them.