The Silver Star decoration and the silver star device on the ETO Ribbon are two entirely different items.
The decoration is awarded for gallantry in action of a degree greater than that deemed sufficient to justify a combat award of the Bronze Star decoration but lesser than that required to justify an award of the Distinguished Service Cross or Medal of Honor. Awards of the decoration to members of the Army and Army Air Corps during World War II were so numerous that it would be impractical - if not impossible - to compile a complete list.
The silver star device on the ETO Ribbon is displayed in lieu of five bronze star devices - indicating your Dad is credited with having participated in a total of six designated campaigns in the Mediterranean and/or European Theaters. The bronze arrowhead device indicates he participated in at least one assault landing.