Are you saying that the code shown in Arduino Reference will not run if used in a C++ platform?
Most of the functions on that page, including those I listed, are specific to the Arduino, and will result in undefined references on any other C++ platform.
So whatever bounce.cpp is, it is using bounce.h as an included library. (Are there "libraries" with 'sub-libraries'? )
The bounce.cpp file is the source file. It is where the methods of the class are implemented.
The bounce.h file is the header file. It is where the class, and it's methods and fields, are defined.
The implementation file, and whatever sketches need to use that class, need to include the header file.
Together, the source and header file make up what the Arduino platform refers to as a library.