I find it hard to believe that Popular Science would make such a mistake, but the author has reinforced the mistake by starting the article with "The dark side of the moon, despite its name, is a perfect vantage point for observing the universe."
But all the quotes from scientists correctly say "far side of the moon".
I know this isn't really "science news" but I couldn't find any other community to share this.
And if you continue the quote:
Which implies that in terms of it being "unknown" saying the dark side is no longer relevant.
Logically you are correct, but human vernacular language rarely confirms to logic.
This is the correct answer. Language often evolves. I had never thought of the dark side as the side unexplored. It was always the side facing away from earth. That’s clearly what the author meant.
The complete quote: