I too thought they meant literally dark lol. Started watching the first ep with my parents and they didn't want to continue because they couldn't see anything.

In general I think this happens because a lot of shows/movies shoot in the day and put a filter over it to simulate night time. I guess it's cheaper to film that way (don't have to pay people over time, use a bunch of lights, etc). I remember reading about it after Nope came out, which apparently was revolutionary because the cinematographer came up with a new method to film during the day and make the scenes pop a lot more.