If he has made the payments, then the judge is concluding that, regardless of whose name is on the title, it is really his vehicle; in a divoroce (or, for that matter, many other legal proceedings), the court can and will look behind the "legal fiction" of ownership to how actually paid for, owns, etc. the property/asset. If the vehicle is really your brother's, regardless of whose name is on the title, then the judge can order this.