Other way around, actually: he started out making constructed languages for fun, realized that doing that properly required inventing the cultural and historical context in which it developed, and then, later, started writing fiction set in that world.
Technically it’s an alphabet, not a language (excluding the keys with actual words on them and not just letters). The letters are called Tengwar and in the lore they’re Elvish letters, but you can use them to write in other languages like English. Even in universe they’re used for other languages like on the inscription of the One Ring, which is in Black Speech.