The comments were made on Discord, not on any sort of Nintendo owned space. Afaik this came to light after their private chats leaked, although they also sent some racist stuff to other players.
Racism is not cool, but Nintendo's reaction to this would be like checking the Twitter post history of every member of the Spanish Eurocup team and removing the win from them the moment you find something not PC.
I think it's too much, thought police and all that, but hey it's their tournament so they can do whatever they want.