Something like this isn't really unexpected. I mean, after the last 3D movie, they already have a lot of the work that goes into the production of a computer animated film done. Characters are already modeled and rigged, sets and props are built and textured, etc. Even looking at the image, it looks like they are the exact same models (even the clothes are the same), just with different textures (not entirely sure on that last point, I'd have to look at the film again).
Basically, the production costs shouldn't be that high if they only have one or two new characters to make and can reuse preexisting sets. Then it's just animating it. Well, I'm oversimplifying a bit, but compared to the last film, this one would be quicker and easier to make.
While the last film wasn't anything stellar, the animation was pretty good. Better than I expected, anyway. I found it entertaining enough to watch. Hope this next short piece is fun, too. Not sure what they can accomplish in half an episode's length, though.