People should keep in mind this is just a demo to raise interest in the project. They lack the funds to complete it on their own, so they couldn't present more than those three characters. Hope they do a kickstarter, there's evidently enough interest on this and they managed to make very well done models and stages, I think it would do very well if they go that way.
No way in hell a small company like Arika is going to make such detailed models, stages (with rain effects and all), an engine and everything just for a joke. They are either gauging interest or being completely dumb.
Apparently the game itself isn't a joke, it will be playable and available at a Japanese event where Kazunoko will play against some selected players. The joke was that they hid the game that was to be played, not that the game is a joke. Also no way in hell they would invest the enormous amount of effort to get those assets done at that high level of polish to make a silly prank.