But the reason the above commenter has a point is because it’s unclear if the claim is false. I know nothing about the game, but the article claims this 3rd party spent so much effort creating a new way of playing the game that the game studio meant to implement those changes and even mention this 3rd party in the credits.

So the commenter is right: this person (apparently) created a work (IP) and thinks they have a right to monopolize that work.

The fact that IP law exists in the first place gives this person ground to stand on and do a lot of damage, because the claim has some amount of truth. There is probably not enough truth to his IP claim that this will work for him, but there is enough truth that he’d be mentioned in the credits.