Perhaps I'm not following, but doesn't that explanation imply that a Tesla's efficiency increase over the average car comes overwhelmingly from reductions in wind and drivetrain resistance? For the numbers to come out this way, that efficiency increase would have to be vastly larger than I would have guessed.
I would have guessed that most of the loss of efficiency (as in the fuel's heat of combustion divided by the displacement of the car's weight) of a gas car was heat loss from the internal combustion engine. But I know very little about cars.
For example: Teslas improve general efficiency considerably by (for example) using regenerative braking, which will be utilised in normal driving but not if you're travelling up a big hill on a freeway.
Furthermore, they're particularly heavy cars - a Ford Fusion (similar sized saloon) is about 1500kg, whilst the Tesla is 2100kg, presumably because of the batteries - the extra effort to lift up a hill is linear in the weight, so it'll be at least a 25% drop in the surplus cost over normal driving.
Overall, it's not really an efficiency thing because the costs of fuels vary so much. For pure heat-to-wheel efficiency, the most important one is that since Teslas are about 80% efficient at turning power into motion, and charge efficiency is about 97%, and a combined cycle power station is about 55% efficient at converting heat energy into power, then the total efficiency from heat to wheel is about 43%, whilst a modern petrol car might be expected to see more like 30%.
I would have guessed that most of the loss of efficiency (as in the fuel's heat of combustion divided by the displacement of the car's weight) of a gas car was heat loss from the internal combustion engine. But I know very little about cars.