While the C++ language is indeed a superset of the C language, the paradigms of modern C++ have almost no overlap with those of C. See for example the string qsort vs string std::sort elsewhere in this thread.

The myth in "To understand C++, you must first learn C" is not that C and C++ are unrelated. The myth is that learning C helps you understand C++. The reality is that telling people to learn C first is an excellent way of getting them to write really bad C++ when they switch over to C++11.