Supreme Court Ruling on FICA Taxation of Severance Payments

The U.S. Supreme Court unanimously ruled (8-0) in United States v. Quality Stores, Inc. that severance payments are subject to FICA tax.  The U.S. District Court and the U.S. Court of Appeals for the Sixth Circuit had ruled that such payments were not subject to FICA tax.    Query how all the U.S. Supreme Court justices could rule that both the lower courts got it wrong?  It shows that anything is possible in the federal legal system.