I think it was 20 percent ineffiecient, as in wasted power probably due to the auto trans used in there testing. Old tranny are or actually I should say can be that bad.
The engine isn't able to extract anything near 100% of the energy that's theoretically in the gasoline. Although around 98% of the gas does get burnt (one frequent claim of scammers is that it doesn't burn all the gas), a lot of the energy ends up going into heating up the radiator, out the exhaust as heat and noise, etc. And that's not even counting the bearing friction, power needed to drive accessories, etc.
If a motor with 10:1 compression had perfectly frictionless bearings, a zero backpressure exhaust, thermal coatings that reflected so much heat back into the combustion chamber it was able to run with no coolant, and a bunch of other things that won't ever happen in the real world, it still wouldn't go over 60% efficiency.