They do explain that in more detail deeper in the complaint. They allege that OpenAI has obtained the offboarding checklist for Apple managers, that OpenAI is using it to issue guidance to departing employees on how they can avoid scrutiny, and that employees receiving this guidance have been ignoring Apple security personnel who try to schedule their standard exit processes.
That doesn't sound too heinous. As far as I am aware, employers aren't entitled to exit processes so long as they get their property back. OpenAI possessing an offboarding checklist accessible to any Apple manager doesn't seem like an IP issue.
I'm not sure what conclusion to draw from this part other than Apple trying to imply OpenAI has something to hide.