As we saw today, RFKJr talks about the rise in autism cases and always claims it's tied to vaccines, a claim conclusively debunked by science. It's tied to something else: the fact that more physicians test for autism today than ever before, and that leads directly to more diagnoses.
Nobody ever accused RFKJr of being bright or even honest.
One factor not mentioned in the rise of autism diagnoses is that parents may need an official diagnosis to qualify their children for free special education programs. This creates a market for testing and could lead to over diagnosing.