Well, maybe I can handle that question. Extruded powders are made by pushing the powder mixture, which is like a dough, through fine holes in a screen. It is exactly like making spaghetti or macaroni, but on a smaller scale. The powder granules look, in fact, like tiny spaghetti or macaroni, as they are short rods or tubes. The gray color is a coating to control burning and feed better through measures.
The other type of powder in common use is ball powder, which is made a different way and is in small balls; these are sometimes flattened slightly. They are similarly coated.
All measures work better with ball powder, but some don't work as well with extruded powder, having sharp surfaces that cut grains and hinder the operation of the measure.