The Japanese name for Sand Rush is Sand Paddle. It's basically a reference to how fiction creatures "swim" through sand as though it were water.
Garchomp is a land shark, so they're obviously not giving it Sand Rush on purpose, as they are with Dragon Dance and its inability to learn Earthquake by levelup.
Really though, I'm waiting for them to replace M-Garchomp's ability with Sand Rush. Now THAT will be a fun day. Excadrill eat your heart out.
