I find that perfectly normal. The fans were apparently making a "Pokémon" game, when this belongs to Nintendo. Nobody wants someone else to release fan games using the same name as yours, creating possible confusion this would be a geniune "Pokémon" game and not a generic, fan "Pokémon-like" game. Had they used a different name and different assets, it would have been fine. Again, this is perfectly normal, and there's nothing new about this - Nintendo had acted like that since the mid 1980s.