Hmm...Where is the confusion?...
Navies do their jobs on the water. The theater of war included the Gulf of Tonkin. One might reasonably wonder how much in harm's way the US Navy was during the VietNam war but then one might wonder how much in harm's way I was while in country. Who makes the decisions and how they make them with regard to campaign inclusion I don't know. But I believe that ships in the Gulf qualified.