As discovered and reported by 404 Media, the information comes via a comprehensive spreadsheet obtained by the outlet, in which Nintendo's regional channels are listed across ten rows. Other major companies listed include the likes of Disney, Rockstar Games, Netflix, and Sony.
An anonymous Runway employee spoke to 404 and stated:
"The channels in that spreadsheet were a company-wide effort to find good quality videos to build the model with. This was then used as input to a massive web crawler which downloaded all the videos from all those channels, using proxies to avoid getting blocked by Google."
Although it's not known whether Nintendo's content has definitively been used to train Gen-3, its mere presence within the spreadsheet will likely spur the company to pursue the matter further. Nintendo is staunchly protective of its IP, and frequently combats instances of piracy that may negatively impact the brand.