An incidence of 1 in 36 rising to 1 in 31 is not a surge of 400%. A surge of 400% would be a quintupling to 5 in 36.
The article is poorly written. The autism rate increase is over the last 20 years. Ser data at link. https://www.statista.com/chart/29630/identified-prevalence-of-autism-spectrum-disorder-in-the-us/