That phrase does not bother me
It poetically describes a part of the moon that we could not see for a very long time - it was dark to us. And to get all techie, it is very dark to a lot of radio frequencies that the near-side shines brightly in.
Dunno if the conceit of the dark-side actually being dark is a construct of the reviewer. Or if it is dark in the show. Certainly don't expect movie reviewers to know any astronomy.
Time will tell.