It's easy to see how phrases such as “terror related” are confusing. As Jackdaw33 says, anyone going around setting fire to things and stabbing people is going to be pretty damn terrifying to anyone in the vicinity.
However, nowadays, the phrase “terror related” means relating to or as a consequence of an affiliation with a recognised terrorist organisation. Unless the authorities can unequivocally link the actions of an individual or group with a known terrorist organisation, the heinous act is classified (in the media at least) as being “not terror related”. This mangling of the English language will – and already has in my opinion - lead to some individual's acts being labelled as “not terror related” when their actions are quite clearly and obviously inspired by their particular religious belief and by extension, the beliefs of others who are actively trying to drag the western world back to the seventh century.
Just because someone doesn't shout “Alahu Akbar” while committing an atrocity, doesn't mean they aren't ideologically tied to an outdated, murderous, death-cult.