"Given a single facial image, a classifier could correctly distinguish between gay and heterosexual men in 81% of cases, and in 71% of cases for women"

I can guess if someone of gay or straight with 98% accuracy - just always guess they are straight.

Tha ratio of gay to straight in the test data set is perhaps the most important part in determining how well the algorithm actually performs.

Are we supposed to assume the computer was shown a 50/50 split of gay and hetero people? It appears that way. But please, tell us.