Humans are not metabolically efficient, yes, but on a bicycle the total transport efficiency is more efficient than anything else, and 30% for an ICE car is in ideal, optimal conditions. Real world stop and go driving is likely closer to 15%.
A human on a bicycle is efficient because of mass and that the bicycle itself is a very efficient machine. A cyclist will burn around 30cal/mile of riding. If a gallon of gas has about 31.5k kcal of energy, then that's about 1,000MPGe for a human on a bike. A 200lb person + 20lb bike requires very little energy to overcome rolling resistance compared to a 2000+ lb ICE vehicle that spends the majority of its energy just to move its own mass.
