Biggest one in this case, in my opinion: it's an extremely long article with awkward section headers every few paragraphs. I find that any use of "The ___ Problem" or "The ___ Lesson" for a section header is especially glaring. Or more generally, many superfluous section headers of the form "The [oddly-constructed noun phrase]". I mean, googling "The Fire-Retardant Giants" literally only returns this specific article.
Or another one here: the historic stock price data is slightly wrong. For whatever reason, LLMs seem to make mistakes with that often, perhaps due to operating on downsampled data. The initial red-flag here is the first table claims Apple's split-adjusted peak close in 2000 was exactly $1.00.
There are plenty of issues with the accuracy of the written content as well, but it's not worth getting into.