"OpenGL" is a bit of a misnomer here, there's nothing directly related to OpenGL. This will not teach you how opengl works, but is an example of a software rasterizer. Knowing how that works will help you understand what is going on under the hood of your graphics API.

This renderer does do lighting per-fragment, so it's more akin to the newer shader-based OpenGL.

If you look at main.cpp the vertex and framgment stages are abstracted via IShader, which also handles passing data between them. This emulates the programmable pipeline.

It will give the educational toy-analogue to a modern programmable pipeline by using C++ code which is more or less isomorphic to shader based OpenGL (or DirectX).