The one I am making is "If a human could eat gasoline, there would be orders of magnitude less environmental damage to do so compared to eating ordinary food"

Humans can't of course, but the guy claiming biking gets 3000 mpg equivalent is making the same comparison.

In truth if we're making atmospheric carbon loading comparisons between traveling by car of bicycle, the equivalent "miles per gallon" would be much closer to equal with cars and biking, especially if you fill yourself up with grain light, produce heavy organic diets.