That Caterham was going about 15 mph though. 131 mpg is not at all surprising or revolutionary at that speed with the right gearing and very low weight.
Take it on the highway, I doubt it would get over 40 mpg. The aerodynamics on the Caterham 7 are crap. Even on this specific Caterham that did some aerodynamic tweaks, it still probably isn't very good in that department. The Cd*A(in ft squared) of a stock Caterham is around 9.0. I doubt this car is lower than 7.0.
However, take that crap 7 body off and put an aero-modded Lotus 11 body on it, with a hard top, and you'd be getting somewhere. That would potentially do 70+ mpg highway with that 120 horsepower gasoline engine and WITH the skinny LRR tires replaced by something a little more sticky and race-worthy.