The facts of English rule over Ireland is well-documented. The particular framing of it as colonization is something that stands out to me is all.

Wikipedia only uses that terminology Sparingly. Again, not because it's not colonization, but because I think most people think of colonization as a thing that white people do to brown people.

The choice of framing is interesting because when you think about it colonization is just invading a place and imposing your citizens as a ruling class and your culture as superior (etc.). There are LOTS of instances of that throughout history that we don't usually call "colonization" (say, the Normans colonizing England), because in practice that word evokes the very specific kind of colonization that was practiced by Europeans from the 1400s onward. So I see insisting on saying that "Ireland was colonized" instead of "Ireland was invaded/oppressed" (both of which are correct) as a way to emphasize the harshness of British rule by appealing to colonial remorse. I don't say that judgmentally, I just find the linguistic aspect interesting.