The pipeline is essentially the same since what the article describes is the architectural abstraction modern GPUs implement. WebGL is essentially only a layer

The pipeline is essentially the same since what the article describes is the architectural abstraction modern GPUs implement. WebGL is essentially only a layer over the system GPU APIs (DirectX, OpenGL, Vulkan, btw the fact you are using WebGL does not mean you are using the OS OpenGL since, for example, on Windows most browsers use a SW component called ANGLE to translate WebGL calls into DirectX commands, due to the fact that the DirectX path on Windows is often more robust/performant) which are implemented by the driver, and thus are the main way to communicate with the HW and drive the graphics acceleration. This being said, you can learn WebGL and especially Three.js without knowing the pipeline as described there, but knowing it will help you understand some subtleties or if you ever want to move to a lower level.