One: the original Axios article requires you to log in.

Two: The researchers were aware of the limits of AI detectors, and tested the one they used. From the article:

We should also take the judgments of AI detectors with a grain of salt, since their reliability is up for question. In its own testing of Surfer’s accuracy, Graphite had the detector analyze a sample of AI-generated articles and another sample of human articles, finding that it labeled human-written articles as AI-made 4.2 percent of the time — a common problem with these tools — but only mistook AI-written articles as human 0.6 percent of the time.

And really, judging from the quality of search results these days, I would have expected a lot more than 50% of new online articles to be AI generated, so from that standpoint the article might be good news 😆