Yeah, no kidding. Besides, aren't the risks mostly just that HRT gives you the same health problems as a cisgender person of your target gender?
Plus, any trans person who's been on HRT has very likely had their birth gonads removed, and won't produce very much sex hormones on their own. Would this study have someone like that switch to taking HRT of their assigned birth gender?
I can't truly say without looking at the study myself, but it sounds bonkers.