I don't know if it is ai generated or at the opposite hand written a little bit fast but I find this article very hard to read despite the concepts in it being simple.
In my mind, slop is when the output is longer than the context provided by the user -- there's text, but there's no content.
Where LLMs can be really actually quite useful, is situations where you have a lot of context and want to distil it. That's what I think happened here: the author has a lot of information to convey, and the LLM-generated output is relatively information-dense.
Unfortunately there's no objective measure for information density of an arbitrary piece of text.