Oh I didn't mean as a matter of compatibility, although compatibility is (mostly) achievable and they share a syntactic and structural origin.

I just think that their names, common syntax and saying things like 'C++ is a [sort of] superset of C' make people unfamiliar with them think that they are more related than they are. That's why I brought up Python and Ruby - two languages that are different in syntax and many details but in the same conceptual space, whereas C and C++ look more similar, sound like almost the same thing but are, conceptually, on different planets.