I think the issue is that there is no such thing as a “biological woman”. Manhood/womanhood is an issue of gender, not sex, and gender is something that we collectively made up whose meaning varies from person to person and from culture to culture. The only person who is capable of saying “Person McFaceface is/is not a woman” is Person McFaceface.
Even if we were to interpret their comment to mean “sex”, that isn’t a simple binary yes/no kind of question. There is no single trait that determines maleness or femaleness, and lots of people have traits indicative of both sexes or of neither sex (or they were born that way then surgically altered shortly after birth), and sometimes those traits are so hidden and so internal that the person themself doesn’t know about it.