This to me is distasteful. Not having a go, not blaming you if this is something you're not familiar with, many people aren't and my knowledge too it's limited.
I don't think we know the full story yet, we may never know. If true that this fighter has XY chromosomes I think the most likely explanation is that she's intersex. In that case her primary sexual characteristics are very likely to be those typically associated with females. Intersex people can have XY chromosomes and appear physically as either male or female from birth.
Calling an intersex person who has identified as a woman all her life, and probably lived most of her life knowing nothing about her genetic makeup, a man is imo not anywhere near ok.
The issues around intersex people and competition in high level sports are difficult and I won't pretend to have all the answers. But this kind of language certainly isn't part of the solution.
Intersex people exist. Some of them are quite conscious about their looks not fitting all that neatly into the typical gender binary. Having people all over the world saying "he's a man", or "XY therefore man" isn't true and can be very hurtful. Potentially for this particular boxer (how could I know for sure), but also for other intersex people. Or even just for people who aren't intersex, but are self conscious about a part of their physical appearance not fitting into the "gender binary".
DSD or intersex people do exist though even if it's rare. They don't fit neatly into the binary. Pretending that they do isn't good, useful or true.