I have a buddy that does CG animation for advertisements. They are done by a third party ad company. They sometimes supply assets for use but usually only minimal, if any at all. Usually left up the the ad company to do all that work.
Welcome to the site, IceGamer! I've heard about this rumored 4-door Mustang for a while, and I've gotta say, I would really like to hear more about this car. There was also a rumor a while back saying that it would be all-electric instead of gas-powered, but I hope for the latter instead.