To be really clear about the definition of terrorism from when anarchists were proud to be called terrorists: "terrorism" is an action during a conflict that is meant to defeat the opposition by creating fear, rather than by removing its physical ability to resist.
Example: If a street gang occupies your neighborhood, you and your neighbors could remove them by 1) taking up arms and confronting them until they take enough casualties that they they have to retreat or surrender, or 2) kidnapping a straggler once every week or so, skinning him alive, recording it on videotape, and hanging him from a lamppost with the videotape around his neck.
1) is an attack on the ability to fight, 2) is an attack on the will to fight.
So IMO Scahill is getting to the essence of it in your reference here.
Example: If a street gang occupies your neighborhood, you and your neighbors could remove them by 1) taking up arms and confronting them until they take enough casualties that they they have to retreat or surrender, or 2) kidnapping a straggler once every week or so, skinning him alive, recording it on videotape, and hanging him from a lamppost with the videotape around his neck.
1) is an attack on the ability to fight, 2) is an attack on the will to fight.
So IMO Scahill is getting to the essence of it in your reference here.