Nope, sand is not grit. It's too fine and is often comprised of softer water-soluble rock, like limestone. It varies depending where the sand came from. Sometimes mixed river sand can be used by chickens as grit, but a bagged product is usually too fine.
Grit is crushed granite or another stone product that says it's "insoluble", meaning it does not dissolve in water. It stays intact in the gizzard so it can do the job of grinding tough food.
Anything that says "substrate" is meant as bedding, floor, or plant growing media.
The term is used across the pet industry and agriculture. From aquariums and terrariums to growing orchids and making hamsters cozy. It's always meant to be inedible but whether an animal eats it is often their own decision, lol.
