So the question is which measure do you consider more relevant: Fuel consumption or fuel efficiency?
Fuel consumption asks "how much fuel do I have to consume to go a certain distance?" Fuel efficiency asks "how much distance can I get out of a given amount of fuel"? If I have a fixed size gas tank (as all cars do), and I want to know how far I can go on that tank of gas, then fuel efficiency -- rather than fuel consumption -- is more important to me.
As shown, "efficiency" as you call it, the distance/volume method, leads to confusion. If it didn't, that trick question test wouldn't have been floating around for so long, with so many people getting it wrong.