You're not wrong, but this amuses me because, in aircraft, "ground speed" means what you're calling GPS speed. Basically just the horizontal component of your speed. An aircraft in a vertical dive has a ground speed of zero even if it's close to breaking the sound barrier.

(For extra confusion, "air speed" is your speed relative to the air around you, and that air may also be moving. If you're in level flight, heading due north into a 50MPH wind blowing due south, you might have a 300MPH airspeed but only 250MPH ground speed.)