At least in the context you supplied this doesn't disprove two genders... It seems as though they were only looking at trans men and trans women (or boys and girls respectively in the experiment with the kids). Now, I don't know the specifics so they might simply not have been looking at anyone outside the gender binary. But all they managed to prove is that gender is not the same as sex, that trans women are women and trans men are men, and that the brain structure difference is already present in kids.
I'd love for them to stick me in an MRI and try to figure out my gender from my brain activity. 🤔