He's just lucky like that?
I suppose the only possible explanation is that he makes really long exposures. How else? Unless NASA make his lenses and his film was manufactured in Zeta Reticuli - which also happens to be where Ansel came from, look it up.
But anyway, Kenna always talks about making day look like night and vice versa. He seeks out unusual atmospheric conditions. Many of his pictures, being devoid of direct sunlight and having limited tonal range could, for all we know, have been shot at night or day. There's very little reference to time of day, which makes his pictures so evocatively 'still'. But due to the practicality of shooting wild landscapes at night, I'd assume very few of his pictures are. It's more to do with his cleverness in the darkroom.