I did read the entirety of the page and am most definitely not being pedantic.
The description that was given regarding a shift to a more "Active Mitigation model" in which tanks were required to be more "active" in their defense is very similar to the model that FF14 has used for quite a while, focusing on low consistent incoming damage with spikes of high incoming damage through things like tankbusters and abilities designed to counter those damage spikes.
This is juxtaposed by the fairly common tanking model that existed before in MMOs in which defense and incoming damage on the tank was more a battle of attrition where damage was fairly constant and defenses tended to be more passive in implementation, relying on stances or passive ability buffs gained through specialization trees and the like.
Basically the concept of the "Active Mitigation model" that they went over was the more general design concept and delineation of active vs. passive and how that plays into encounter and ability design. Active being abilities that are designed to be activated in response to periods of spike damage and passive being the stuff that just kind of happens in the background that tends to help with just general survivability and lessening damage consistently and being relatively constant over a long period of time.
The more refined idea of "Active Mitigation abilities" that evolved in Legion is something that I also touched upon in my initial post on the matter, pointing out the evolution and implementation of such abilities in FF14 as well with IB, TBN and Sheltron.
WoW just went all-in to one extreme (surprise ... surprise ...) on the conceptual implementation of Active Mitigation, shrinking the breadth of mitigation and highly focusing it into one ability that needs to get used over and over.
FF14 on the other hand did a more measured and mixed approach, where they kept the idea of a number of varied mitigation abilities, paced out by cooldown times but still having relatively shorter durations to be used to counter moments of spike damage but also layered in the short to no cooldown time abilities with very short durations which are gated by other things such as resources akin to what WoW did in Legion.
Both are methods of Active Mitigation design, just with variances of implementation. Spread out or consolidated.
Active mitigation is not determined by it being a part of a rotation, although an ability that provides defense that is part of a rotation can be Active Mitigation.
I feel the confusion likely comes from the implementation in Legion where mitigation was so consolidated, that it resulted in one ability being used over and over regularly and thus being factored into being a part of your standard rotation. This was probably compounded by many of the early implemented abilities along this vein having the mitigation aspect tacked onto an offensive ability.
This is only one heavily skewed implementation of what Active Mitigation can be and by no means is the very definition of it.
So again I state, Active Mitigation is when mitigation is designed to be actively engaged in response to damage and attacks, whereas Passive Mitigation is mitigation that is designed to simply exist passively and fairly consistently without real extra thought or engagement on the player's part.
It is these such variances in design and implementation of Active Mitigation that caused me to ask that people not just generally throw the term around without better defining what they mean.
Also, I think it goes without saying that falling to ad hominems such as calling someone pedantic doesn't strengthen your argument.