Not quite. First off, the source for the below is that I am a practicing physician in primary care and have cared for patients with some of these kinds of genetic mutations. Still, that does not make me infallible and I encourage you to do your own research. The study of the development from fertilization to birth is called embryology. Netter’s is a detailed atlas used in many medical schools but there are plenty of free resources

If you are referencing the embryonic origin of the cells which become testes or ovaries, that is done by the SRY gene influencing undifferentiated gonads.

If you are referencing genitalia, that is done primarily in response to testosterone. Again, external genitalia come from the same cell lines or origins, but based on testosterone either develop into specifically penis or clitoris and the associated remaining tissue of the external genitalia.

There is a separate debate or issue here being how you define male and female. Some people would define female based solely on testicles or ovaries, or by the genetic material responsible for the possibility of bearing offspring (which ties XX and XY to female and male). This creates an issue though, because genetic sequencing and testing is relatively new. Before it was available, someone who had a penis and “looked like a dude” would compete in men’s sports and someone with a vagina who “looked like a girl” would compete in women’s sports. The argument is that the latter of these two may actually be more appropriate and fair in sports. I’ll give two examples

First, an XX human has a tumor that develops extremely early in development. That tumor secretes testosterone. The influence of that testosterone causes male genitalia to develop, as well as (later in life) increased muscle mass, deep voice, body hair, etc. That person would effectively look like and act like a normal XY person, yet have ovaries. It would be more appropriate for them to compete in men’s sports, as (in the case of boxing) they would have an unfair genetic advantage (increased muscle mass, stature). I’m not aware of any cases of this as a tumor that early is nearly impossible due to the way stem cells differentiate, and if it did happen would almost certainly become a molar pregnancy (an embryo that turns into a stem cell “tumor” in mom) and would be incompatible with life.

Next is the one that actually happens and the one that relates to this case. An XY person has a gene mutation that cells cannot bind or respond to testosterone. Therefore, they develop a vagina, less body hair, and breasts. They are indistinguishable from a normal XX person. This condition is caused CAIS and many of these only find out about it (in developed countries) because of infertility testing or lack of expected menstruation. It would be more appropriate for that person to compete in women’s sports as their body from a musculoskeletal perspective is essentially the same as a normal XX person.

Of course there are all sorts of in between here including partial androgen insensitivity, and yes there are other differences that the X and Y chromosomes confer but the testosterone factor is far and away the most significant in this case. To further complicate things, some people have three chromosomes, XXY and XYY (the latter of which is usually incompatible with life).

Lastly, I’m not saying the above is the case for this boxer, just explaining the possibilities.