Why call the subtended angle a pixel, instead of something else ?
In most cases, a CSS pixel will be equal to a device pixel. But, as you point out, the definition of a CSS pixel will sometimes be different. For example, on a laser printer, one CSS pixel can be equal to 3?3 device pixels to avoid printing illegibly small text and images. I dont recall anyone ever proposing another name for it. Subangle? Personally, I think most people would prefer the pragmatic px to the non-intuitive sa.