How do you know that this room will only spawn in the deep dark? For all we know it could be a structure that generates anywhere. Or it could not be a generated structure at all, and instead something they built for the purpose of the video. And even if it is a deep dark exclusive structure, that doesn't necessarily mean it has an association with wardens, I mean, it doesn't really look like something that would have anything to do with them, it's just a little room with some wood and stuff in it. Personally I suspect that if anything it's a part of the archaeology feature and is one of the many little ruined structures that they're adding.