It can get confusing.
I use the term AF Override because that's what it's really doing. You have your normal AF area set, and when you press a programmed button, it overrides to a different AF area - but only as long as you press. When you release the button, the camera reverts back to the normal AF area it was using prior to the press. If you could tap a button and have the camera switch to the program AF area, then it's would be switching, but as it stands, when you release the button it goes back to the current normal AF area - I don't know how to describe that beyond on override
The real trick comes in because a handoff is a subset of AF override. In both an override and handoff, you are temporarily changing AF areas; but with an handoff you are picking up at the exact AF area the camera was just using. That's not the case with overrides. As I mentioned in the video, all AF handoffs include an AF override, but not all AF overrides include a handoff