Certain patterns are much more common in LLM output than in human writing. I'm a journalist and love an em dash, for example, but I've never met/read another journalist that uses them nearly as often as LLMs. Same with the "this isn't just X, it's Y" pattern. When you have multiple of these patterns in every paragraph, it's a pretty clear indicator that the text is AI-generated.
Plus, the author admitted to using AI to write it.
One of the little tics I've noticed that helps weed out and LLM generated text is to CTRL+F and look for the word "therefor" in any of it. LLMs will use the word in a new sentence that isn't the conclusion of any previous sentences or paragraphs. Think like, "Bees are small fuzzy and yellow. Therefor their ability to fly is an astounding achievement." In all of my years of reading I've never seen people use the word that much in common writing, and when they do it's usually as part of a compound sentence. These things really do have their own little set of semantics and dialect that they follow that seems like it's a unique quirk.
Plus, the author admitted to using AI to write it.