It's not!
https://twitter.com/chrizmillr/status/341968821730549760
"LIVE ACTION SHOOT"
Also:

You're loving stupid. This film has been in production for 4 years already, and you believe that the entire thing was made in 5 days? Because if you want to base all of your information on that twitter message, that's what you're implying.
The movie has SOME stop motion, however the majority of the film is CG. (see:
http://en.wikipedia.org/wiki/The_Lego_Movie#Production "Australian Animal Logic will provide the animation, which is expected to comprise 80% of the film. ")
It's much more efficient to make a film that adapts to the frame cutting of a stop motion than it is to produce a real stop motion. And, trust me, if it were a real stop motion, those gaps would be far from as noticable as they are in the trailer -- this is far from a small budget.
You don't really know much about cinematography OR the film we're discussing, so quit spouting information which is based on your childish speculation.
And, on that note, if you actually think the random lego pictures have anything to do with the film's production, you're really loving stupid.