This should go without saying but terrorism isn't just any violence that makes you feel terrified. Terrorism is defined by the motive of the attacker.
Yes, and to add another wrinkle: What if an attacker is inspired by ISIS or "incel" subreddits but is also severely mentally ill--autism, schizophrenia, bi-polar--can we truly call it terrorism? I don't think so b/c the attacker doesn't fully appreciate what he is doing.