He had increased contrast by using a red filter, so the scene or the light has not been changed. No clouds copied in, no selective greyscale changes on parts of the image, just during paper exposure selective exposure time. No tens of layers, each with selective manipulations. All those changes apply essentially to the entire image. Compare it with what have been seen on the lula pages, like this ocean scene (australia?), where a person has been copied in, because actually noboday wanted to stand there, or this river bed in which dramatic early morning sun light has been copied in. The difference between half dome, in which only contrasts of been adjusted, on those are obvious to me. There is a difference between adjustments made to overcome the limits of the negative and paper etc. and those which just creates situation, which didn't exist.
Drawing clear lines always has something arbitrary, but that doesn't makes them obsolete. Think of state borders, official languages etc.. They are arbitrary, but have been made for good reasons. Using color filters in color analog photography is also a manipulation, but it has it limits and can enhance color to properly translate the real lighting situation on film and paper. If you create a colorful sunset, which hasn't been colorful at all, it is a manipulation which goes too far.
This is where painting starts.
One has to discriminate between techniques, which help to translate a situation, with which one tries to overcome the limits of the techniques and those which create something, which has only been in the mind of the creator of the image.