In a way I don't believe Nintendo was naive enough to rely on 'pinky promise'. Nintendo makes you sign NDAs for getting information about unreleased games, going to events, and playing review copies. Usually not personally, but there's a contract between Nintendo and the news / writing org.
So I'm pretty sure they did this with the foresight that people would start talking about it. How they can see that as a net positive I find hard to argue, but they get datamined on the regular and games are leaked a week before street date so they had to know.