I consciously chose "men" both to parallel the construction of the headline "Boy", with the specific intention of having the sentence hit home for those HN readers who see themselves as "men", while quietly tapping into a certain sexist bias ^1 I've observed in both American medical practices.
Under normal circumstances, I would agree with your point, and I would likely have selected either "transwomen" or "bio-males" in this scenario. Both are exclusionary for various reasons ^2^3, and when making my selection I came to realize that all possible phrases I could use here would result in some sort of HN reply thread about the word or phrase chosen.
Technically, the most correct phrasing for the sentiment I was expressing clocks in at 26 words: "People seeking estradiol treatment for body dysphoria who are perceived as 'men' by their prescribing doctor, regardless of their self-identified gender or their physical sex characteristics". However, that itself would have resulted in a reply thread about shorter ways I could have expressed that, and encouraged a discussion about weakening the accuracy of transgender representation for the convenience of others. That would do more harm than good to transgender acceptance at this point in time than I could accept.
In the end, I considered it most productive for the guaranteed-to-occur HN tangent about my choice of phrasing here to focus on how the word "men" in transgender treatment contexts is insufficiently representative, rather than to focus on how the most-correct phrase is overly representative.
In review of the replies, I am content with the results of my choice. Many users are realizing that there is no simple wording to express this concept, and that every possible choice has issues. It will slightly improve empathy and understanding of transgender representation issues. I feel this choice of wording has been successful.
^1 Doctors are more likely to seek informed consent for procedures affecting reproductive systems (including E2/T dosing) from those they perceive as "men", regardless of the person's actual 'sex' or self-identified gender, especially when the side effects would affect virility in a fertile male.
^2 Genders that are not "women" are permitted to treat body dysphoria by increasing their estradiol levels, too.
^3 Short for "biological males", which excludes people who are not simple 'XY males', such as hermaphrodites, that for whatever reason choose to treat body dysphoria with estradiol.