At 0:49 the back of the device can be seen. However, it was never modeled or even mentioned in any previous video. What am I missing? Did you accidentally upload the videos in the wrong order?
I think the question is rather: The back of the device has the cartridge pack already modeled, but in the previous video we did not model the cartridge pack. I'm still making my way through the course, so I am not sure if the cartridge pack is modeled later or not - but it's possible that a video is missing.
EDIT: I just noticed the next video is called "Creating the Cartridge Slot" so I think we are good to go ahead and keep modeling. My guess is that it was a simple oopsies in the order of making the videos.