That only reduces the storage volume. Without that you would need to drive a blimp.
At that density in the storage tank, it can be close to the same energy density per unit volume of diesel, but you cannot have intake cycle of the engine operating at 10,000 psi or you will not be able to take in any air for combustion.
Well then...sounds like the dude is full of schnit. Going by the article, it sounds good, though. Then again, I did make a B in physics. 60 mpg would be nice at $4.00 a gallon, though.