In almost all fighting games, when you block an attack, your hitbox is fixed to the hitbox of whatever guard animation for the duration of the guardstun. So if you guard an attack high, and someone followups with an attack that normal whiffs if you're crouching, but doesn't whiff if you're standing, the attack won't whiff. Regardless of if you are crouching.
A simple example is something like,
With Ky, do a stunedge>FRC>IAD j.S
and have someone block the stunedge standing, then immediately go to a crouch. If you do it right, they can't crouch the j.S to make it whiff.
The term originated from 3D games, and got mangled on it's why to 2D games. In 3D games, it means something completely different.