The 3D perspective page http://webglfundamentals.org/webgl/lessons/webgl-3d-perspect... clearly describes the rasterization phase as having 3D: the automatic perspective divide and the triangle clipping to a 3D space. Clip space being 3D seems very strange if WebGL is only a 2D API.
My suggested patch would be to rephrase it for the beginner. "WebGL is largely a 3D rasterizing API and not a fire-and-forget scene rendering solution."
If WebGL were only 2D it would be trivial to implement 3D without shaders in <canvas> -- and that is not true, canvas cannot rasterize 3D triangles.