He was using the AI to help him extract quotes; it makes sense that, as the head AI writer, he would be experimenting with new AI tools to become more familiar with them. It sounds like he just got confused at some point at mixed up a paraphrasing of the AI tool with an original quote, and it sounds like he was not in the best shape when writing this article so he made a dumb mistake. Regardless, arguably the use of AI here is a red herring, because if he had double-checked his quotes and fixed them then it would not have mattered whether he used AI or not.

I think that damning his entire career over this would be too extreme. I suspect that his will be a very good learning experience for him, but that unfortunately he will need to apply his lessons at another place of employment.