It sounds a bit like something I saw in a BTS video about the Hobbit films where Peter Jackson walked around an empty room with a steadi-cam and it added his movement to a 3D environment that he could see on the camera monitor. Essentially it allowed him to move freely around this CGI scene with realistic camera movements. I’m guessing ILM have made something similar for this show. The term “in camera” seems weird to me though, but it could simply mean that they can see the CGI extensions on the monitors while they film. However, I can’t find any reasons why they wouldn’t just film the actors on green-screen and then add the backgrounds in post. That would certainly work better, unless there’s some new technology I’m not aware of which can remove green-screen flawlessly “in-camera”.

I was a bit surprised at his comparison to the Lion King sets because all the footage that has been shown so far has mostly been real sets. Though since all the videos online has such poor resolution I guess most of the far-off backgrounds could have been made using this technique.