What does the C device mean?

Basically it just means they received the award in a deployed setting. You don't have to actually "see" combat or participate in it. The combat C device is earned "through service or achievement under combat conditions."

Basically, just being deployed to a combat zone.


https://www.army.mil/article/184881/new_combat_related_devices_authorized_for_decorations

It means that every kid gets a trophy. It ranks up there with a growing list of "Thank You For Playing"
Once, I was in a NATO School in Weingarten Germany Called the International Long Range Reconnaissance School (ILRRPS). It was attended by all the member armies of NATO. One afternoon, a British Soldier From the Recce platoon in 2 Para noticed that several of us Americans were answering most of the questions. In Class he then made the following statement: "Roger, if you get three more right, the US Army will give you another medal." It was the running joke at ILRRPS that the US Army gives out more awards and decorations than any other NATO country.
Soon we will look like those morons with the huge hats in North Korea and that would be just Turble...Turble Turble Turble....To look like Kim Jong Un (With appologies to both Charles Barkley and Frank Caliendo)

It was a way to satisfy the crybabies who wanted special awards (i.e. drone operators with the R device) and other award hounds.