[user104658]

In his father's own words on why he targeted women: "Because he wanted a girlfriend, he had no social skills and he was very frustrated".

So yes of course he was also mentally ill, but this is 100% an incel-motivated attack and I would be very, very surprised if there aren't incel groups and boards in his Internet history.

For me that makes this 100% terrorism. Attacks on women driven by Internet ideologies and indoctrination are terrorism. Pure and simple. As surely as any religion.