Sorry if the title is a bit confusing, I'm a bit confused myself. In the past I have used SDL, and SDL2 which uses OpenGL(when specified). I've set a rather tough task ahead but wanted to challenge myself to not use a full fledged library like SDL2 and instead attempt to use C++ and OpenGL (again without the help of SDL2).
Could one say "I wrote this with C++ and OpenGL" if they were using GLFW or is there an even lower level to access OpenGL? I guess what I'm trying to ask is. Do the majority of people who develop in OpenGL use GLFW and GLEW or can you go straight to the "OpenGL library"?
A fair number of independent games developers who want their games to be cross platform and want to write their own engine use SDL to get their OpenGL context. That said, if you're using an OpenGL context directly, I think it's perfectly reasonable to say you're using OpenGL, even if you use another library to get it.
Hypothetically, for each OS, you could just use their native functionality to get an OpenGL context. Please note that approach is (obviously) not cross-platform, and on Linux, if you use GLX, will tie you into software that is becoming obsoleted*.
-Albatross
*Technically GLFW support for Wayland and Mir is experimental at the time, but it's still being developed.