They didn't call it "OpenGL". They called it "OpenGL ES". The ES is a significant part of the name. The fact that the name happens in part to contain the word "OpenGL" is not a promise of source compatibility, and even the most cursory glances at the documentation would have made it clear that the API has a different name because it is a different API.

It's incredibly daft to argue that part of a name amounts to a promise of backwards compatibility with a different API, in perpetuity. The X11 protocol isn't backwards compatible with that of X9 simply because they both share a name-fragment.