Idk. If someone can pinpoint a single cause, it is binary. Not that I think that's possible: the human mind is so poorly understood, a real cause-effect relationship is scifi.

> some people are barely distracted by loud noises ...

It's not an argument for a non-binary classification. The whole point is that that a symptom, even a group of symptoms, doesn't define autism. Sensitivity to noise is just one of those things that some group has managed to be associated with autism.

Its definition has been expanded significantly. If it continues, there'll be two types of people: autists and psychopaths.