Without a political reason it's just a large scale murder.The number of victims is irrelevant to have it classified as terrorism.
Same way a terrorist attack can have no victim at all.
Murders can still terrorize people especially when you have lots of victims or when it happens really close to where you live.
I understand what you're saying.
Personally, I just disagree with the political "box" this term has been placed in. Murder, if done out in public, to me, is also terrorism. It was an act done to incite terror among the people.
But again, I'm not Merriam or Webster, so my personal definition may be just that, personal.