I’ve heard that stance used for abortion, so I assume it’s a statement trying to equate consensual sterilization (which shouldn’t be required to transition, but sometimes is) to the history of nonconsentual sterilization of people of color in America.
Now it’s a batshit take, but I’ve found transphobes tend to use whatever legitimate grievances they have against anybody and slap it on trans people.
The only way in which I can try and make some sense of it would be if a black person, who's mostly in an environment where there's mostly black people, and therefore the majority of or the only trans people they know are black, thinks that non-black trans people are insignificant, and that trans people can't ever have children.
Personally, I'm grading this conspiracy theory with a F. Grifters used to put in more effort back in my days.
It's roughly the same as swatting criticism of the Zionist Genocide by claiming that said criticism is anti-semitic - it conflates two quite different groups (in one case Jews and Zionists, in this case LGBT and Blacks) in order to weaponize the humanist moral position about the treatment of one of those groups to stop criticism of immoral actions by or (in this case) against a different group.
This is quite a common element of the gaslighting which is so typical of Liberal politics (a very common example is female liberal politicians defending the kind of legislation that will hurt the poor claiming that criticism of their position is due to their gender), though this specific example is an especially exagerated and ridiculous version.