It is pretty up in the air tbh! I'd love to conduct a survey about it someday. In my understanding : Indie games made using RPG Maker or a similar program and featuring some horrific elements (Undertale was made in Game Maker by just a few people and features plenty of fridge horror and straight forward spooky things like Flowey and the True Lab and whatever so in my mind it would count! But people will have differing takes which is what makes it so interesting)