I am pretty sure that is referring to content xD The res of a panel is kinda fixed on a hardware level haha. The native res of a panel is in essence how many pixels are in the panel, ya can go to a lower res but you cant go higher as every pixel can only display one pixel, whereas if you go to a lower res the pixels can be combined.
bit confusing but its actually quite simple, too bad I dont have a diagram
EDIT: Put it this way, the display is essentially stretched across more pixels when you use a lower resolution, however when you go to a higher resolution you are essentially asking the pixel to take on the job of more than one and since pixels can only be one color at a time that would make it impossible.
EDIT2: please just ignore the first edit, just seems to make it more confusing at times haha.