That 5x comparison is against polymer solar cells, which as you mentioned are less efficient than silicon. Although less efficient, the polymer cells are (or will be) cheaper to produce and more flexible. Still, this stuff could be even more efficient than silicon so there is a lot of potential here, especially for portable electronics.
If they want to argue efficiency, then they must compare their best to the industries current best. And the current state of the art is the poly-crystalline PV cells which is 2.5x more efficient than the numbers they offered.
--Boot Hill