Carbon neutrality means carbon dioxide neutrality. Carbon is just an element and literally everything you see and don't see has some of it in it.
Also, around 2% of our sun's energy production involves the Bethe-Weizsäcker cycle which is a cyclical fusion reaction using carbon, nitrogen and oxygen. (The main source of energy production is through a proton-proton chain since our sun is too small to rely on the CNO-cycle entirely)
I'd just prefer to tell them how to get rid of carbon in their bodies, and if they looked up the process they would get the real info about it dealing with carbon. It's not my fault they don't know the context of what would happen when the carbon goes away.
@MishaVelthuis Carbon is the element that allows life to exist, as it makes the planet warm enough for liquid water by contributing to the greenhouse effect.