To be clear, Turn 10 didn't make this naming convention up or something.I could be wrong with this game, but that means the developers are using the english language incorrectly,
if they are first rendering at 8k and then scaling to 4k then they are scaling it at 50%, not 200% like the game states.
8k scaled by 50% = 4k, 8k * 0.5 = 4k
i.e. in a logical step list
step 1. render at X resolution
step 2. scale image
step 3. display that scaled image
As I understand it, this is just how DSR is read.
100% is native to your display device (or your current display resolution). This is baseline metric. Since that could be 4K or 1080p, or 1920x1200 etc.
Anything higher than 100%, is a % increase in both X and Y axis.
Displaying 200% of native resolution is double your native.