It's like finding a couple dozen people with the flu, feeding them chicken soup, and then reporting that a month later they feel healthier, so the soup must have helped. Maybe it did, maybe it didn't, but you didn't measure that so you don't know.
According to this professional medical trial, the recorded ASD scores are "based on the Childhood Autism Rating Scale (CARS) rated by a professional evaluator"
You should have specific knowledge of that evaluation in order to criticize it as relying on "subjective questionnaires" and shouldn't introduce doubt by simply stating something as "given".