I'm not entirely up to speed on US law, but wouldn't OpenAI have to provide the court some kind of proof that they didn't use it in the training data during discovery?
It’s not been decided if training a model on copyrighted works is “okay” or not as far as I know, but I expect it to be so, given that literally everyone does so at this point. It’s not like imagenet is copyright free, many of the images were/are.