"Ça va." translates "It's going well", not "it is".
Similarly, "Ça va?" translates to "Is it going well?".
It's as meaningless an exchange as most greetings (the only meaning being to actually acknowledge and greet the person), but it does mean something literally, and the exchange is technically more complete than when answering "How are you?" with "Hi".
That being said, you'll see someone answering "Salut, ça va?" with "Salut!" quite frequently as well. I would perhaps consider it slightly more of a misstep than in English, but only marginally so.