I don't see it as confusing, it's a pretty accurate description. The Nix language is for most part a JSON-look-alike with a couple of additional features. You don't really program in it, you declare/return a data structure. The only programming you do in Nix is to make it a little easier to build that data structure. It's kind of like the old days when people would parse JSON with eval(), which would also grand you features that plain JSON wouldn't have.

Even NixOS itself doesn't do all that much actual programming in Nix, most of the code that does stuff is written in C++. The Nix language itself doesn't let you escape out of its sandbox.