I have little doubt Charles I would have labeled Oliver Cromwell a terrorist. I have little doubt James I would have labeled Guy Fawkes a terrorist. Definitely, the British establishment labeled the IRA as terrorists even before they blew up Mountbatten's yacht.
Here comes the soapbox.
Let's use Mountbatten's yacht. Mountbatten was the last viceroy of India. He was a royal. He was definitely a part of the British establishment. And, the establishment was suppressing Northern Ireland.
The IRA planted a bomb on Mountbatten's yacht. One of the dead was a young man--maybe 16-18 years old. A nephew--I don't recall for sure, but its all easily google-able. The point is there is almost no way this young guy could have been involved in the British suppression of Ireland. Yet, the IRA blew him to pieces as part of their attack on Mountbatten.
"Oh! I think its tragic that a handsome young man who had nothing to do with the suppression of Northern Ireland was destroyed by those terrorists in the IRA!!"
Oh, really? The Brits criticized the IRA for not agreeing to the rules of civilized warfare--killing innocent non-combatants? Really?
In suppressing Northern Ireland, the British government essentially said to Northern Ireland, "We don't care whether you agree. Your ideas don't matter. You will do what we say just because we say so."
So, where did the British government get standing to complain when the IRA said back, "Oh, thank you for setting the rules--agreement doesn't matter. If you can use force to inflict your ideas on us, then it is necessarily fair for us to inflict our ideas on you without your agreement."
What? The Brits wanted to claim it was uncivilized to kill the youth? HA! They themselves authorized his death!--by saying it was OK to use force, including lethal force, to force their ideas on others. At that instant they also said, "Force is what counts. Not ideas. Not agreement. Not consensual persuasion." The youth's death was totally legitimized by the Brits themselves: if agreement doesn't count, if agreement isn't necessary, then the IRA didn't need British agreement before blowing up the boat. I'm not saying murder is legitimate. I am saying the British government has no standing to criticize the IRA--because they themselves said his killing was legitimate.
So, how is terrorism defined by the author cited in the OP? Or, more importantly, who is doing the defining?