From the linked article:
"We can be certain that autism rates have gone up for artefactual reasons—diagnosis, changing awareness and incentives, etc. rather than real increases in the number of people with autism—by exploiting policy changes. For example, above, I mentioned the Massachusetts saw autism reports increase 400% in one year due to a change in school reporting."
This is exactly the issue that I'm getting at, which is shared with the above user's assertion. We cannot be certain of any of this. Especially not because of some handpicked examples by the author. None of this is provable or falsifiable, even if a the handful of disparate examples picked by the author seem compelling. Besides the examples of reporting changes, the author's arguments almost wholly rely on untestable counterfactuals.
Also:
"A single piece of evidence indicates that there is no real epidemic of autism. As remarked in a review in a 2020 Nature Reviews Disease Primers article:
No significant evidence is available supporting that autism is rarer in older people, which provides further evidence against the suggestion that autism is increasing in prevalence over time."
This doesn't provide evidence of anything. The absence of evidence does not constitute evidence. This is just an argument from ignorance. This is little different from saying that there is no significant evidence that people 500 years ago had lower rates of being diagnosed with a given disease, therefore the rates of people with that disease were likely the same as now.