A gallery can't switch off that instinct to judge quickly. What it can do is add something right after the first glance. A visitor sees a photograph, then reads a story which includes identity and strengths, but also difficulties, support, development and challenges that may remain today. Maybe a behavior that looked strange sat next to an interest that later became a career. Someone might have needed a lot of support in one area and become completely independent in another. Perhaps a teacher or a parent noticed something everyone else missed. None of that shows up in a face.
There's also the simple problem of timing. A behavior arrives before any context does. Someone avoids eye contact. Someone talks with an unusual rhythm. A child stares at one object for a long time. Watching this, people often jump straight to a conclusion, like rude or incapable, without anything to check that conclusion against.
A stereotype doesn't have to sound unkind to do damage. The idea that autistic people are unusually gifted sounds like a compliment, but it quietly sets a bar: be exceptional, or you won't be taken seriously. Most autistic lives don't fit that image any better than they fit the opposite one, the idea that autistic people can't manage much at all.
Media matters here. A review of autism in fiction, published in the journal Autism, found the same patterns showing up again and again: mostly white, mostly male characters, and the "autistic genius" trope returning film after film. Portrayals have gotten a bit more varied lately, but the overall range is still narrow [3].
Most people don't build their picture of autism through years of knowing a wide range of autistic people. They build it through TV, film, school materials, medical language, social media, and maybe one or two people they actually know.