That makes a lot of sense. Intuitively (I haven't tried to run numbers on this), the big efficiency problem with a car – gas or EV – is not that it's using "unnatural" forms of power, it's that you're hauling a 3000 pound vehicle around with your 160 pound human. It's easy to believe that photovoltaic power -> modern battery -> electric motor is far more efficient than photosynthesis -> animal digestion -> human digestion -> human muscle. I wouldn't be shocked if that held up even on a vegan diet, though the difference would be a rounding error compared to the emissions from other aspects of our lives.