4:3 TV and 16:9 video signal:
Letterbox: Inserts black bars at the top & bottom part of a 16:9 picture to "convert" it to a 4:3 one.
Pan & Scan: Zoom in a 16:9 picture to fit the whole height in a 4:3 screen, and of course you lose some left & right parts of picture.
Just Scale: Resizes 16:9 picture to fit 4:3 screen, so picture loses its aspect ratio.
16:9 TV and 4:3 video signal
Pan&Scan, (you're right. it should be called another way, like f.i. "Zoom"): The 4:3 picture is zoomed in to fit the whole widht in a 16:9 screen, and of course you lose some top & bottom parts of picture.
Pillarbox: Inserts black bars at the left & right part of a 4:3 picture to "convert" it to a 16:9 one.
Just Scale: Resizes picture to fit screen, it loses aspect ratio.
That's the theorical behaviour of set top boxes.
The problem comes when Pillarbox and Pan&Scan (Zoom) are exchanged in Display 4:3 content as.... settings,