C++ is an almost perfect superset of C. (using the term "perfect" in the "superset"-ness of c++, not its design quality.) From this perspective, it is appropriate to lump them together.
I see plenty of people who claim they write "C++" but end up writing some mutant "C with classes" C++ is not just "C with addons", it's a different language that happen to share its syntax and part of its standard library. Lumping them together leads to ugly C++ code.