This reads like the article author has never heard of software 3D-renderers before
This particular one happening to be run on a microcontroller (personally I find calling this a "GPU" a stretch, given the microcontroller just so happens to at the current moment be running software that outputs IO that the screen-side controller can interpret as input).
I should mention that the "written from scratch" part (that isn't commonly written in 3D-renderer implementations these days) really is primarily just a couple-hundred lines of point, line and triangle-fill drawing code (that substitute the original OpenGL calls the creator used previously). (Actually outputting the buffer to the screen was done using a pre-existing library.) The implementation of meshes, transform/projection matrices, a 3D-math library, physics, ... is all basic game/graphics programming that is commonly written for/along-side 3D-renderers (anybody that's followed decent e.g. OpenGL and game-dev tutorials has likely implemented these).
I congratulate the person on succeeding with this project (unironically
) and the article author for having managed to pass this as TH-tier news.