He's not some junior developer with his first job, he's the senior editor. If a senior editor plagiarized an article, he would rightly be fired because it's a serious violation of journalistic ethics. He knew using AI tools like that was against company policy and he did it anyway. That's well beyond just making a mistake.
The story is called "The Big Hack" and was run by Bloomberg in 2018. All the major companies named in the story conducted investigations and never found anything, but the story was never retracted.