That is actually what i thought you were asking, and i don’t know the answer.
The closest i can get is that RYB was used.
If you put in #09A7A1 in paletton and press opposite, you get #FF790E
The major advantage of Paletton is it’s not using the modern computer and engineering RGB color space, but it’s built on a classical artistic color wheel, applies classical color theory and works within a specially created RYB color space.
Looking at this issue on github, this may be part of some inconsistency in the curriculum.
I haven’t done the math to confirm this, i only used the paletton tool and the info on the paletton wiki. However, if this is the case, then it should be corrected.