IMO, the answer is no. You can go to different areas within any state and see distinctly different traits in mustangs. There is inbreeding in many areas, just like line breeding, and they will have very similar physical traits in a given area
. Mustangers freshened the blood often, so that was a lot of "localized" freshening of the blood. Whatever unique traits that it is claimed they possess, thay are not "standard" and cannot be consistantly reproduced from 2 randomly selected mustangs taken from 2 separate areas - and their lineage has not been recorded - hence, cannot be considered a breed.