Here's an absolutely wild detail!
To use paired articles on the same topics, they started with human-written articles and then had AI generate articles of the same topic and length, so it had to make up names for people in the stories, and it used the same names ... a lot:
"Annotator 1 is the only one to pick up on 'AI names': in fact, 63.3% of GPT-4O and 70% of CLAUDE-3.5-SONNET articles include either the name Emily or Sarah."