It was in a court filing: https://storage.courtlistener.com/recap/gov.uscourts.cand.40...
also the discovery of the list was a strong rebuttal to the (iirc) CEO of Midjourney complaining that finding the source of online images in order to ask permission / offer compensation was just too arduous a task and also that they didn't bother. Well here's a list of thousands of artist styles they bothered to identify.