Sorry, I worded that backwards. I should have said that as an aircraft speeds up, the coefficient of drag decreases. Yet a sphere, or racecar for another example, will not change their Coefficient of drag as speed changes.
However, I can see this is not an apples to apples comparison, since an aircraft in level flight will change it’s profile to the air (as Beagle pointed out via a Coefficient of lift change), while a sphere, or racecar won’t.
Hawk