Game categories are controlled by IGDB and then ingested by Twitch
if a game category is not normally injested by Twitch (such as a Mod) uservoice is used to request a category to be created for that game.
If you want a game that is a Mod created as a category please request it via uservoice
https://twitch.uservoice.com/forums/310210-discover?category_id=367945