I think you are only getting half the story.
The real story is that a "pro" can travel from room to room and quickly understand how their brain and ears are acclimating, and then they can do lots of good work.
But it probably doesn't hurt that the speakers on the desk cost $20k or $30k.
And hey, he may be running ARC. :-)
You should get some photos of the other rooms he works in before you focus on this bedroom studio as if it's some sort of proof that there is no benefit to acoustics management.
I'm a big fan of Mr Vigs catalog... its seems to all be close mic'd heavy pop. Love it!
If he had a quiet singer or acoustic guitarist in there... he'd have traffic noise bleeding in just like everyone else and he'd have the sound of the room, and has been mentioned the resonance of the drum kit... etc. etc.
Heck I've been mixing at my kitchen counter with auratones for a few weeks because I like the view out the window. It's springtime here and the leaves and flowers are at their best.
I check the mixes in my real room.
best regards,
mike