The folks who consider WebGL as a 2D API include some of the the browser developers who implemented it. That said, I don't fully agree with them. If WebGL were simply a 2D API, this example, from a talk I gave way back in '13 wouldn't work. In this example, one triangle is clearly drawn behind the other using only raw 3D coordinates with no projection yet.
It also isn't a fully 3D API either, otherwise we wouldn't have to be so concerned about the order in which we draw transparent objects. This is the result of using a 2D drawing surface plus a depth buffer.
That said, it might be too subtle a point to open with. Especially since you are showing code, the understanding of which requires material that they haven't covered yet.
http://www.vizitsolutions.com/portfolio/webgl/animatedWalkth...
It also isn't a fully 3D API either, otherwise we wouldn't have to be so concerned about the order in which we draw transparent objects. This is the result of using a 2D drawing surface plus a depth buffer.
That said, it might be too subtle a point to open with. Especially since you are showing code, the understanding of which requires material that they haven't covered yet.