Autism is more broad-spectrum than just related to social processing. It's most visible in social processing because that's the cognitive area that humans have highly specialized in as a species, where expectations of performance are very high, and thus where deficiencies processing complex information in real-time are most visible. If we were birds, we'd probably think autism had something to do with flying. Instead, we are talking tribal apes, so when someone has the cognitive differences that lead to autism, we notice most strongly that they are having trouble being a normal talking tribal ape.
But the effects of autism are visible outside of social interaction too, with repetitive behaviors, intense focused interests, trouble with adapting to change, rigidity in lifestyle, etc.