Yeah, basically they used the eGFR (a measure of how well the kidneys are functioning) for the sex the individual self reported. The Male and female reference ranges are different and so treatment was based on the wrong measure - the person had, at the time I read the article, stage four kidney disease which is basically end stage - the kidney does not recover from that.
It’s worth pointing out as well that testosterone given to a female also strains the kidney.
Sex does matter very much sometimes in medicine. Some viruses seem to affect the sexes differently for example. Other conditions present differently in men and women (heart attacks being one example.)
Biology matters.