In a culinary setting you'd be right, in a road salting setting it's slightly more complicated.

You can get very fine halites (rock salt as you say) mined as an alternative source to sea salt.

Council gritters (clues in the name) use rough mined rocksalt which is mixed with sand and other aggregates and usualy screened to ~ 10 mm to make it amenable to spreading this definitely does contain small stones and grit and is why you get gritty sandy buildup on roads during gritting season that won't wash directly away when it rains (as a motorcyclist this is a nightmare as it tends to build up on crosshatch and makes filtering extra dangerous.

I agree it's not particularly helpful we just use rock salt to describe both materials though.