The article begins with a story, ironically, of a woman who has demonstrated through several pregnancies that she has a female reproductive system. She is an example of mosaicism. This condition does not make her trans.
The rest of the article is mainly about intersex people. Intersex people are not trans, they have a biological sex and suffer from disorders of sexual development.
Intersex people have repeatedly asked not to be used as a "gotcha" for the TRA movement, they find it deeply upsetting. I would have thought, as the TRA movement places the importance of Hurty Feelings above everything in the universe, that they would have immediately desisted from using people who have repeatedly asked not to be used as a "gotcha." How strange that TRAs don't seem to care about the feelings of intersex people.
Now, if trans identity was indeed scientifically and biologically linked with (say) mosaicism, or an intersex DSD, or an MRI-scan showing a pink/blue brain, the obvious thing would be to carry out the appropriate test for these in order to provide certification of trans identity.
Yet, surprisingly, tests or any other form of "gatekeeping" in favour of Self-IDing by magic incantation because gender identity is to do with your deepest innermost authentic-est feelings that cannot possibly be gainsaid.
So which is it? Biological physical basis (hence testable prior to certification) or metaphysical incantation that is superior to physical reality (hence unquestionable, and deserving of immediate affirmation by the universe)?