Reading the context in the linked Twitter, this is not actually the list used to train. After the model was already trained, they scraped this list of artist n

Reading the context in the linked Twitter, this is not actually the list used to train. After the model was already trained, they scraped this list of artist names off Wikipedia and did some optimizations so that prompts using them would render faster. The actual model was trained on everything, whether it had a Wikipedia page or not.