"Monopoly" is just a shorthand for a range of market dominance abuse. I.e. if an 800lb gorilla abuses you, it doesn't really matter that there are several others 600-700 lb gorillas ready to do the same to you.
"A dominant position is not defined merely by market share, but by classification as a market leader. Typically, a company is considered to hold a dominant position if it has a market share of more than 40%, but even a market share of 15% may be considered dominant if it is the largest player in a fragmented market. "
I think they're saying that the word "monopoly" is used colloquially, by many, to simply mean dominant position and that those people don't mean the literal definition. It seems they're just trying to say that the parent comment is arguing about the definition of monopoly rather than the actual point, which is dominant position abuse.
I agree that it's important to recognize the differences between monopolies, duopolies, and oligopolies in theory and practice, as you say, but I also don't think that using the wrong term nullifies validity of the actual point.
https://ethique.rexel.com/en/competition-law/abuse-of-a-domi...
"A dominant position is not defined merely by market share, but by classification as a market leader. Typically, a company is considered to hold a dominant position if it has a market share of more than 40%, but even a market share of 15% may be considered dominant if it is the largest player in a fragmented market. "