Even if something wasn't written by ChatGPT, I'm supposing ChatGPT's influence on writing has been so strong that (1) any typical reader of text on the internet will have ingested a lot of ChatGPT writing habits in their own writing, and (2) that any reader of ChatGPT text is so habituated to those writing habits that even non-ChatGPT generated text appears similar to ChatGPT generated text.