I feel like this is a willfully confusing article. So autism may involve disrupted genetics, but you may not have inherited those genes from your parents, they may be what are called "de novo mutations" which are mutations to the sperm or egg cells in the parent. This is evidenced by autism being more prevalent when the parents are older and those mutations are more common.

Also it clearly must be to some degree mutations if you believe the rates are going up, which even the government is no longer disputing (though that may not be conclusive proof, to me it seems evidence leans to more likely than not currently).

De novo mutations can also be caused by environmental factors, this is very well established and called "genotoxicity"[1] and certainly some people have been exposed to known genotoxic chemicals to varying degrees over time (formaldehyde) and who knows what undiscovered ones there are, newer standards of pesticide testing are starting to look for reproductive health effects but many chemicals that have been in use for a long time haven't been held to the highest standard.

Another reason you might think it would be "de novo" mutations is that this could be any sorts of random errors in the genome. If autism is an umbrella label for various genome errors (which it very well may be, since it correlates with other conditions very often), that may explain why it's so hard to pin down a few genes and why symptom expression varies so drastically.

1. https://en.wikipedia.org/wiki/Genotoxicity