I wonder how have they measured it... But in any case, one might argue that truly human writing will (already is) a competitive advantage - depending on the domain of course, we do not always care about that
I think that long, tedious, vapid text is AI written. Pithy, deeply insightful materials I assume are written by humans.
These days, I just delete and move on if the "article" doesn't deliver interesting and meaningful content within the first half page or so.