to go back home = to return home in English.
It is the English in question here. Physically, this means returning to a place where a person was previously. "I am going home" (Voy a casa) doesn't give the sense of a round trip that "go back home" and "return home" (vuelven a casa) both relay.
A casa and en casa are usually translated "home".
Vuelven a casa. They return home,
Voy a casa. I'm going (I go) home.
Estoy en casa. I'm home. I'm at home.
Ven a casa. Come home.
Quédate en casa. Stay home.
If volver means to return then why did they "go back" instead or "return to"
I would think that would be "mas tarde", or something to that extent.