Looking at the camera list and the fact it doesn't need new firmware, they're probably just using the existing tethering preview functionality.

The same can be achieved with gphoto2 piped to v4l2loopback (using ffmpeg to transcode). Something like:

    $ sudo modprobe v4l2loopback exclusive_caps=1 
    
    $ gphoto2 --stdout --capture-movie | ffmpeg -i - -vcodec rawvideo -pix_fmt yuv420p -threads 0 -f v4l2 /dev/video0