The article you referenced "Defining Terrorism:
Is One Man’s Terrorist Another Man’s Freedom Fighter?
by Boaz Ganoris" is accurate in its definition of Terrorists and groups of Terrrorists. The article rightly defines Terrorism based on three critically important elements:
1. The essence of the activity—the use of, or threat to use, violence. According to this definition, an activity that does not involve violence or a threat of violence will not be defined as terrorism (including non-violent protest—strikes, peaceful demonstrations, tax revolts, etc.).
2. The aim of the activity is always political—namely, the goal is to attain
political objectives; changing the regime, changing the people in power,
changing social or economic policies, etc. In the absence of a political aim, the activity will not be defined as Terrorism. A violent activity against
civilians that has no political aim is, at most, an act of criminal delinquency, a
felony, or simply an act of insanity unrelated to terrorism. I also add ideological aims to the list of political aims. The motivation—whether ideological, or political is relevant for the purpose of defining terrorism. In this
context, the following statement by Duvall and Stohl deserves mention:
Motives are entirely irrelevant to the concept of political terrorism. Most
analysts fail to recognize this and, hence, tend to discuss certain motives as
logical or necessary aspects of terrorism. But they are not. At best, they are
empirical regularities associated with terrorism.
3. The targets of terrorism are always "strategic" and aimed at innocent people (civilians, noncombatants, public servants, military not engaged in hostililites e.g. 'USS Cole'.) Terrorism is thus distinguished from other types of political violence (guerrilla warfare, freedom fighting, civil insurrection, etc.). Terrorism exploits the relative vulnerability of the civilian “underbelly”—the tremendous anxiety, and the intense media reaction evoked by attacks against strategic civilian targets.
4) Terrorist activities transend boundaries where as insurgencies are local within kilometers of the insurgent's base of operation.

The paper does not discuss insurgencies but makes reference to violent activity against civilians that have no political aim as acts of criminal delinquency, a felony, or simply an act of violence aimed at chaos.
1. The essence of the insurgency activity—the use of violence to create chaos and to disrupt lawful activities within a community. According to this definition, an activity that does not involve violence, extortion or a threat of violence will not be defined as an insurgency (including non-violent protest—strikes, peaceful demonstrations, tax revolts, etc.).
2. The aim of the insurgent activity is never political —namely, the goal is not to attain political objectives; changing the regime, changing the people in power, changing social or economic policies, or even winning the "war." It is however, aimed at protractedness and disrupting the lawful act of governance. A violent activity against civilians that has no political aim is included in the definition of insurgency. It is never an ideological struggle. Most analysts fail to recognize this and, hence, tend to discuss certain motives (sectarian, religious, tribal) as logical or necessary aspects of insurgencies. They are not. At best, they are attempts to incite others into the chaos by breeding hatred, mistrust and playing on strongly held belief systems such as religion. That is why religious entities are often targets.
3. The targets of insurgencies are targets of opportunity and "tactical" and although aimed at those that are associated with restoring law and order --they will include attacks on innocent people (civilians, noncombatants, public servants inorder to ensure protractedness. It is the protractedness that provides "Utility" to the insurgent population. Insurgency must also be distinguished from other types of violence (guerrilla warfare, freedom fighters, etc.) and others that have political aims. Insurgencies exploit the vulnerability of security and lack of security for civilians given that a government cannot secure the entire community at the same time.

In the end, it is important that we separate the two in order to effectly understand and engage each.