Exactly. As I stated before, if we neglect all forces except air resistance then:

F (i.e. the drag force) = Cd x Area x (air speed)^2

Power = F x v (i.e. ground speed)

So if you're sitting still, then your ground speed is zero and it takes no power to stay in place even if there's a substantial wind (in a really strong wind there will be some internal muscle energy losses to overcome just to hold on - but no actual external work is done in a physics sense).

So from the standpoint of power required, there's a big difference between sitting still in a 20 mph wind vs. moving at 10 mph into a 10 mph wind.

For your original example I worked out the math in the previous post - going 10 mph into a 20 mph headwind is about equivalent in power required to going 26.2 mph with no wind (assuming level ground and no other energy losses). So that's part of the answer. The other two parts are that the wind speed close to the ground was probably less than 20 mph and that there are other drag forces (rolling resistance and mech. losses) in addition to air drag.