People are posting something like 350,000,000 pictures each day to Facebook, so human review is pretty much out of the question. The sure-fire way to avoid the problem is to avoid Facebook.
Despite all the progressive virtue signaling, tech companies tend to wield the disciplinary and censorship hammers harder against queer content compared to equivalent cisgender or heterosexual content. How much of it is purposeful or due to unconscious bias is hard to say. Did the algorithm know this was a pride event? Did it detect the rainbow ascot on the man in the suspenders? These things aren't transparent to the public. It's hard to say whether that is even what happened here and I don't want to jump to conclusions. I just wanted to point this out.