A local mill seldom has the capability to grind the raw materials, (corn, soybeans, sunflower seeds, and/or other grains) add the vitamin/nutrient package, mix, and then pelletize. Those pellet aren't cheap machines. To make crumbles, crush pellets as desired. Larger farms have a feed mill on site, be it for hogs, dairy or poultry. Lately, people have been buying grain mills for their home, grinding their own grains for cereals, baking and the like. These table top models aren't cheap, however.
Mash is an old fashioned word. It is merely coarse ground feed. Not quite as fine as people think. But, since it is ground fresh and mixed and bagged locally, yes, it's "dusty", although flour coated might be a more accurate expression.
Just how fine the mix is ground is the choice of the mill, of course. But in any case, when you add some water and stir, you can see that mash looks a bit like granola or a chunky grain cereal.
For centuries, feed has been ground at the mill. Human food too! The advent of pre-bagged feed that is trucked about the country is a relatively recent innovation.