Is “The Bull Demon King is an original demon king in 'Journey to the West' with no religious basis.” true?

In Chapter 004 of "Journey to the West", the Bull Demon King and Sun Wukong become sworn brothers, and he styles himself the Great Sage Who Levels Heaven. In neither Buddhist nor Taoist scriptures is there any deity with this title or image; it is entirely the creation of the novelist. The original text: "此时又会了个七弟兄，乃牛魔王、蛟魔王、鹏魔王、狮驼王、猕猴王、𤟹狨王，连自家美猴王七个。" (Chapter 003 of "Journey to the West")