The point is that the 3D-geometry portion of the pipeline is still done on CPU with these early cards. The API's may have been slightly broader, but the hardware accelerated part was limited to rasterization, i.e. painting 2D triangles.
As I explained in a sister comment, there's a lot more going on with rasterization, even back then, than "painting 2D triangles" might imply. Yes, only the XY coordinates determine the screen location of a rendered pixel, but the Z coordinate even at that stage has a lot to do with its color (e.g. for perspective-correct texture lookup) and whether it is painted at all (Z buffering).