It does not define the display or viewing environment.
Every image encoding standard defines that. PQ is not special.
That is a meaningless statement. Just like presenting sRGB at 80 cd/m² outside of the sRGB reference viewing environment is wrong, presenting content following BT.2408 at 203cd/m² outside of its viewing environment is just plain nonsense.
Trying to present what I wrote as “actschually technically incorrect” does not help your argument. You were complaining about luminance, not about primaries.
Linking to a website summarizing that different video standards do in fact require different viewing environments doesn’t help either.