Let's unpack this a bit, shall we?
Nintendo, which isn't big on Xbox-like Achievements, does have an Achievement-like system built into the 3DS.
The 3DS' achievements primarily reward users for networking their system to others'. You get commendations when your 3DS wirelessly connects to a bunch of other 3DSes that are registered to people from other countries. You get them for "meeting" the same person('s 3DS) a bunch of times in a row. Stuff like that. You also get accomplishments recognized for feats in the system's Find Mii game.
The Find Mii RPG programmed into every 3DS is lightweight and wonderful. It's basically the kind of lightly-social, 1-minute-of-delight, vaguely-interactive experiences that most Facebook game designers say they're trying to make. Find Mii is composed of a series of rooms that are guarded by one or two bad guys. Into these rooms, you bring the Mii avatars of people whose 3DS' have come into wireless proximity with yours. The more you cross paths with someone, the more powerful their Mii is. Most of the people I cross paths with as I'm commuting through New York City are first-timers, so their characters are weak. Their characters struggle in Find Mii and usually only do 1-3 points of damage. And sometimes they miss. Sometimes they miss their target three times in a row.
Congratulations! Congratulations to the people whose Miis joined my system and then lost. Congratulations, Nintendo is saying, to whichever one of you out there just had their Mii whiff three times in a dungeon battle in my 3DS. I get a reward for you failing me.
Thanks, Nintendo! Thanks for being so happy about me losing. The confetti was a nice touch.
(And, truth be told, this is one of the best Achievements I've ever received in a system, because it's just so bizarre. The weirder the better, I say. Sorry, I know this is Anger Management and I'm supposed to be angry, but how can I stay mad at a system that's holding a party for me when everything goes badly?)