It’s a measurement of energy needed. Bodies are going to take different amount of force to move the thing, but it’s also going to take a different amount of time, and impart less inertia, which starts averaging out to the same amount of calories. I bet they also raise the amount of calories shown to account for no process being 100% efficient.

Measuring how we consume our calories is also a bit tricky, the bike tells you the minimum energy you spent moving the wheel. It could be slightly more, but not by much because our bodies are pretty efficient at using stuff to burn into energy. The amount needed to move the bike is about as much as we’ll burn because there isn’t a lot of waste. Of course if you have a condition, or are out of shape this changes and the counter becomes more inaccurate, but in a positive way. (You burned more than the counter said). Some will record your body mass index and other info to try to shift you in the right average.

We still calculate how much calories are in food by burning them and seeing how much energy they emit (heat). It’s not really how we consume calories but very similar. All in all calories aren’t a great way to think about human strength, or exercise