In Steven Shapin's review of In a Different Key, he claims that Autistic children's eyes "are not windows to their souls, but black mirrors." Actually, I'm Autistic and since I was a child, I've had completely ordinary-looking eyes--irises, pupils, and so on. I've known a lot of Autistic kids and adults, and I can testify that none of us have black mirrors for eyes.
Some people don't do much communication through eye gaze, which is presumably what Shapin meant. Many Autistic people don't make eye contact because it hurts us. Blind people don't make eye contact because they cannot see. Some people with other disabilities (like Parkinson's disease) cannot control the motions of their eyes. I've met all kinds of people who don't make eye contact, but I've never met anyone whose eyes I would describe as black mirrors. It sounds like something out of a horror movie.
Now, this is some figurative language, so maybe I'm missing the point. I'm Autistic, after all. But I think and think about this phrase, and all I see is some very negative, dehumanizing language aimed at children with a developmental disability. In an article that contains several pieces of misinformation about Autistic people, "black mirrors" is the icing on the cake.