A dunalino is a palomino with the dun gene. Dun is a basically a modifier. Even horses that are just called "duns" are actually bay duns, or bay with a dun gene.
A dorsal stripe is well defined and dark, as if drawn on by a Sharpie. Countershading may be dark, but the edges are fuzzy and generally look like the two sides of the horse are overlapping.
Does that make sense?
And the stallion would have to have dun somewhere to be a true dunalino. If he doesn't have zebra barring or shoulder barring, then it's countershading. Do you have a picture?