Diesel engines are very efficent; a while back, I was looking into a TDI jetta, and its surprising how good of a milage you can get on that thing.  However, its mileage is creamed because they build them in the US to meet all the pollution standards, and the pollutant restrictions in California are stupidly high. 

However, reading the quote at the bottom of the article, I can't tell if its a joke, or if hes comparing the work effiency of the engine itself.