Well okay, so I'm getting a bit off-topic with the whole "food is inefficient" argument, but if you look at the efficiency of photosynthesis it only harvests about 3%-6% of the light energy hitting the plant. A lot of that energy then goes to growing other parts of the plant that don't contribute to its caloric content (stems, roots, etc., or in the case of fruit, the entire rest of the plant besides the fruit). To get a ballpark idea of the numbers here, even biofuels have been found to be only about 0.3% efficient at converting sunlight to chemical energy, compared to solar panels which can typically harvest about 10% of the incoming sunlight into electrical energy. Plants are just not that efficient in general.

But efficiency of converting sunlight into energy isn't really what this argument is about, since we're more concerned with the CO2 output than the energy efficiency. The efficiency of human muscles factors in though, as it is only around 20%, compared to electric motors and batteries that are over 90% efficient. Regenerative braking is a big win for the electric car too, since it reduces the impact of the car's higher mass a lot. And when you look at the CO2 per calorie emitted by coal (and of course the US grid emissions are much better than this since we use many other better energy sources than coal), you get about 1.1g per calorie for coal compared to about 4.8g per calorie for fruit. So in a carbon emissions sense, food can also be much less efficient than electricity, even when that electricity comes from fossil fuels.

No single one of these factors is enough to tip the scales on its own, and of course the numbers can skew either way depending on what kind of food you eat, what kind of electricity you use, and many other factors. But I don't think the comparison is a totally crazy one.