First you can believe that a report comes to conclusions that are correct without believing the report itself. So yes, I believe that racism is depriving black people of the opportunity to become published SFF authors.
(And depriving me of the opportunity to read their stories. As a white cisgendered male, what’s important is how it affects me.)
A bit more detail about, e.g., how you determined whether an author was black would have been useful to give the report more methodological rigor.
Also, statistics is tricky. If a magazine publishes 100 stories, none of them by black people, then you can’t immediately say P = (f_nonblack)^100 and start a boycott. If all 100 stories are by a stable of 5 authors who wrote 20 stories each, then the odds are P = (f_nonblack)^5 which is considerably more likely to be consistent with chance.
So I expect that if the data are re-crunched with this in mind you will find: SFF and the society it inhabits is still a racist hellscape, but with fewer zeros in the probabilities.