Earlier quoted context omitted.
Though there's a sense of the word "dark" that means it's unseen or that we are ignorant of it. Like "to leave someone in the dark", to "go dark" in communication, or a "dark match" in pro-wrestling (it happens but isn't broadcast and doesn't effect storylines). Might be too much to hope for, but he could just mean it's always dark to us. I'm getting of a kick out of this Trone calling it the "backside of a moon" and…
The linked clip is pretty unequivocal, if you watch it. Nelson says: "They are going to have a lander on the far side of the moon, which is the side that is always in dark. We're not planning to go there."
I could see governmental types having a colloquial use of the word at times like these that doesn't mean "it's always in the literal absence of light".