All psychiatric disorders ARE neurological...i.e. is rooted in the brain and associated systems. Moreover, there are plenty of neurological differences between ASD and TD groups, both at the cellular and morphological levels. However, a lot of the morphological differences are too small, and heterogeneity too large, to be useful as a means of diagnosis.
It's entirely possible that there is nothing neurologically objectively different about an autistic person from a non-autistic person, and that it's simply a cultural quirk that led to it; this has been the case with many historical diagnoses.
In fact, I would argue that this is not simply possible, but likely, given that usually, if such a neurological discriminant exist, it is typically quickly found. That they have searched for so long without being able to find it, is indicative of a nonexistence.
Nevertheless, the biggest claim is trying to claim that some behavior/symptomology/quirk does not involve the brain.
Oh, I'm pretty new to this myself, but my understanding was that autism was considered a neurological disorder, not a psychiatric one. [1]
"Autism spectrum disorder (ASD) refers to a group of complex neurodevelopment disorders..."
1. https://www.ninds.nih.gov/Disorders/Patient-Caregiver-Educat...
Many are diagnosed with “autism”, seemingly not for any lack of ability, but præferences the diagnostician does not necessarily agree with.
I also object to “neuro-” morpheme. The diagnosis of these conditions are psychiatric, not neurological, and in many cases where such a diagnosis was made, there is nothing neurologically unusual that could be found, but in some cases there is.
Autism is simply with the current understanding not a neurological, but a psychiatric disorder. — the understanding may grow such that it might become one one day, but that is not the current level of understanding, and such understanding would most likely lead to the realization that all which is currently grouped under “autism”, has many different underlying neurological causes.