From what I know, OpenGL on macOS is internally implemented using Metal and supports more features than ANGLE.
ANGLE on macOS supports OpenGL ES 3.0 when running using Metal backend (source: https://github.com/google/angle), whereas macOS natively supports Core 4.1.
And from my experience, there is basically no difference in performance between Apple's implementation and ANGLE, especially for simple things like what the author is doing.
I don't have internal knowledge of Apple's implementation but it could potentially be layered on top of Metal for Apple Silicon (probably not for Intel) though if so it probably uses internal-only capabilities not exposed to Metal users.
OpenGL ES 3.0 is newer than OpenGL 4.1. The feature set is broadly very similar. Native macOS OpenGL is a backwards compatibility feature and not intended for new development. Lack of KHR_debug and general bugginess makes it a poor choice for learning OpenGL or deploying software on. On the other hand, WebGL is currently supported and extensively tested, with much better validation and error messages and much (much, much) better cross platform compatibility.
ANGLE on macOS supports OpenGL ES 3.0 when running using Metal backend (source: https://github.com/google/angle), whereas macOS natively supports Core 4.1.
And from my experience, there is basically no difference in performance between Apple's implementation and ANGLE, especially for simple things like what the author is doing.