There is also the fact that automatically generated content predates ChatGPT by a lot. By around 2020 most Google searches already returned lots of SEO-optimized pages made from scrapped content or keyword soups made by rudimentary language models or markov chains.

Well there's also the fact that GPT-3 API was released in June 2020 and its writing capabilities were essentially on par with ChatGPT initial release. It was just a bit harder to use, because it wasn't yet trained to follow instructions, it only worked as a very good "autocomplete" model, so prompting was a bit "different" and you couldn't do stuff like "rewrite this existing article in your own words" at all, but if you just wanted to write some bullshit SEO spam from scratch it was already as good as ChatGPT would be 2 years later.