They are being sued by the SFC, which has been deputized by the actual copyright holders to act on their behalf: https://sfconservancy.org/copyleft-compliance/#linux
Except in this case, SFC are not suing on behalf of copyright holders, but as a third-party beneficiary of the GPL contract between copyright holders and Vizio.
Except in this case, SFC are not suing on behalf of copyright holders, but as a third-party beneficiary of the GPL contract between copyright holders and Vizio.