Additional/alternative categories can be requested via the Twitch Uservoice.
https://twitch.uservoice.com/forums/310210-discover?category_id=367945
And IIRC P5royal preceeds the IGDB aquistion and the use of IGDB as the data source for Categories.So likely was made as a category as if it was requested via uservoice as it had been stramed to before how categories are born was changed.