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.
