To be fair, the article did actually suggest an etiological difference between "high-functioning" and "the most severely disabled" cases.
From TFA:
"Investigating the most severely disabled autistic individuals you almost always discover damaging genetic mutations or early life trauma, such as foetal alcohol syndrome. These are clear cases of biological dysfunction. On the other hand, the less severely disabled individuals (who would once have been called Asperger’s or “high-functioning”) show none of those biological signs of dysfunction, instead showing evidence we expect from functional adaptations: the associated genes are common and complex, brain differences are subtle, the characteristics appear early in life when they are guaranteed to affect reproduction, and the prevalence is high enough that at least one person per Dunbar-sized hunter-gatherer social group of one hundred and fifty would show the same traits – in which case, every one of our ancestors would have known an autistic person. These biological signs are those we expect to see from adaptations, not dysfunction. The question we are led to ask is what autism’s function could have been."
From TFA:
"Investigating the most severely disabled autistic individuals you almost always discover damaging genetic mutations or early life trauma, such as foetal alcohol syndrome. These are clear cases of biological dysfunction. On the other hand, the less severely disabled individuals (who would once have been called Asperger’s or “high-functioning”) show none of those biological signs of dysfunction, instead showing evidence we expect from functional adaptations: the associated genes are common and complex, brain differences are subtle, the characteristics appear early in life when they are guaranteed to affect reproduction, and the prevalence is high enough that at least one person per Dunbar-sized hunter-gatherer social group of one hundred and fifty would show the same traits – in which case, every one of our ancestors would have known an autistic person. These biological signs are those we expect to see from adaptations, not dysfunction. The question we are led to ask is what autism’s function could have been."