Of course you are correct about the set-top box, however the rest of the diagram should still stand.
Without the information I am guessing a little bit. Also I don't know if the analogue signal has been switched off in his area. I do believe there are still some areas on analogue.
I'm trying to be not too technical for the OP. Not saying that Chrissie is stupid, just some of it is not in her comfort zone.