He is a handsome fella. However, I am going to make up a new name to use rather than "mutt" since that seems to have a negative connotation. Your rooster is a fine example of an MBC. MIXED BREED CHICKEN. Hey, you have an MBC rooster, LOL!
I have a friend that has roosters that look just like that. Years ago, she ordered an assortment from a hatchery. They have all been mixing and interbreeding since then. Now that is what her boys look like. I would say he is definitely "mixed race."