https://www.nytimes.com/2020/07/05/insider/capitalized-black...
I think it was rather nuanced. Several reasons given:
1) The capitalization of Black has already been accepted by the mainstream - NYT is catching up with the times
2) Other names on American minorities with a shared heritage is already capitalized, like Latino and Asian.
3) African-American is capitalized, but not as inclusive as Black.
At no point, except when referring to some early 20th century worldview, are they talking about all black people worldwide. I read the article as a purely American POV.