[belorn]

I would guess they refer to the suggestion that gender is determined by the genitals that a person is born with, which the parent comment think is correct. Just like the article however, I agree that science has debunked that theory. Androgen insensitivity syndrome for example prevent the masculinization of male genitalia in the developing fetus with male phenotype. They are described by science as XY female, but does not have ovaries or a uterus.

There is also studies done on neuroscience of sex differences, which found that transsexual individuals tend to have the brain characteristics and structures that do not match the genitals that the person was born with. Again a rather strong indication that gender and genitalia do not always match. There is quite a lot of research that indicate transgender as caused by biology, where individuals get a mix of both male and female traits, and genitals in those cases is simply one of many traits.

[eyelidlessness]

I gave you an upvote because this is all important information and likely helpful for other readers, but unless I've misunderstood the parent commenter I'm not sure this is what they meant. All of this information is consistent with the article author's claims, which the parent commenter disputed.

[belorn]

Yes. I was a bit unclear but I was trying to addressing that the top parent comment disagree with the article and think that genitalia determine gender and that there is no science that disproves it. The article is right however that science has pretty much proven that gender is a multitude of traits, and as with any other collections of biological traits those does not always align in every individual.

I edited the post slightly to hopefully make it more clear.