From the article:

“A total of 178 out of the 3,078 articles came back as flagged for AI … About half of our staff spent a month during summer 2025 painstakingly reviewing the text from these 178 articles…

Far more insidious, however, was something else we discovered: More than two-thirds of these articles failed verification. That means the article contained a plausible-sounding sentence, cited to a real, relevant-sounding source. But when you read the source it’s cited to, the information on Wikipedia does not exist in that specific source.”