I think this has less to do with the quality of the text and more to do with whether people have standards or not.
For every person who reads a paragraph of AI text and is instantly disgusted, there are probably 10 or more people who will gladly read pages upon pages of the sloppiest slop imaginable copy-pasted straight from chatgpt.com without batting an eye. That's just how things are, most people have very low standards.
Getting any of the current codemaxxed models to output natural text without obvious AI-isms is not an easy feat, and I doubt this person you mentioned has somehow cracked the case.