I guess the person is implying that for something to be of the Yuri genre, it would have to be something that's geared to an audience looking for girl-on-girl related-stuff, meaning the fact that Yuri-stuff is incidental to Murcielago, it shouldn't be considered "Yuri."
I don't really agree with this though, but I guess we all define things differently.
I think that's what the first responder was implying, but not the second. I think the second was referring to the frequent criticism of a particular way of writing female action characters as basically "men with boobs." That is, the author gives them all of the behaviors, vices, strengths, weaknesses, and so on of a male hero, but the form of a sexy woman. Oftentimes she's the token "girl who's as good as the boys" on an otherwise all-male team.
In this case I kinda think the critcism fits - Kuroko lusts after and approaches women sexually in a way that is utterly unrealistic for women to do, and of course has an affinity for causing pain and violence that is also very atypical for women. She behaves in almost every way like a male character in her role would. She's also physically imposing and, of course, by virtue of her pathology, devoid of any of the emotional traits that are often associated with female characters.
But of course, under no circumstances can you pretend this story is striving for anything like realism. Did the Kuroko character have to be a woman? No. Would anything really have changed if she were a man? Other than the Virginal Rose arc, no. Does it matter? Not especially. The artist wanted to draw lesbian sex, and that's just fine with me. :)
This is a very narrow minded way of looking at things. Basic human emotions and morals (or lack of) are not exclusive to any one group of people.
Trying to define a character like Kuroko, who can be a ruthless butcher or a goofy homemaker depending on the page, by some supposed measures of masculinity or femininity is downright comical.