"one gram of his weight over a kilometer of flat road at an expense of only 0.15 calories"? That can't be true. I weigh 70Kg, and I'm pretty sure I don't expend 10,000 calories riding a bike for a Km.
The calories we tend to think of aren't the same as the calories that we think we know. In regards to energy intake and eating food, a calorie is actually a kilocalorie. So your 10,000 calories to ride a kilometer is actually 10 kcal.
Unless they meant literally a calorie, not the more common large calorie or kilocalorie. In which case they'd be claiming that 1km ride burned ~10 calories, which is at least at the right order of magnitude. I weigh 73k, and according to my watch I burned 136 calories riding my bike for 6.4km yesterday, for an energy usage of 0.29 calories (not kilocalories) per gram-kilometer.
Calorie is a frustrating unit. When talking about food or exercise, usually we use the kilocalorie but just call it a calorie. I assume the previous poster was using the small calorie. See https://en.wikipedia.org/wiki/Calorie.
So, that seems low to me. I would expect you to burn more than 10 kcal, but it seems the right order of magnitude at least.
