As a rule of thumb, any attack, killing, murder, blast etc. that is considered terrorist, it is organized by a government. So, the key element here is government, not organization unless we fully agree that organizations are part of governments, formally or informally.
This is not to say that very rarely people organize killing and murder. I’d say it is highly improbable due to the British form of governance that is applied worldwide, which is a political system that is obsessed with control and infiltration of spies, but even if an attack is organized not by a government, that is not going to be publicized in the media at all.
Again, we live under a political system that the world has never seen: its control is unprecedented and its network of spies is one of its kind. Therefore, by virtue of hearing the word “terrorist”, it means we are dealing with something organized by the government, more precisely, a government which has been approved by the British Empire itself, in other words, all the governments of the world.
Why would governments do that? This is a completely separate question, but I believe that every child who is able to tell the difference between apples and oranges has a somewhat idea of the reasons why a government – a British form of governance, would organize a terrorist attack.