He's a professional writer. As the article says, even if you write your own words, this is still a problem with proofreading, copy-pasting references or quotes, and "AI checkers".
I still don't get why a professional writer would ever accept an AI proofreader over a real one, or a "quote" returned from an LLM over one sourced from a reputable reference.
Is the concern that the AI will rephrase the text during proofreading, thus falsifying a copy-pasted quote? I'm not sure how such a change could go unnoticed, unless you blindly publish the AI output without looking at it, which doesn't sound like something someone would do who wants to “write their own words”.