Which part of the two backgrounds do you mean? The dark one, I guess?
What did you do to the photo in PS?
Did you partially brighten it?
For there are two light situations severely competing with each other and I would just guess that in the original photo the bright part "won" and the dark half was much darker.
If you pull up brightness in PS (or any pp software, for that matter), it is like you sort of change the ISO settings for that part of the picture. You get noise.
This one was a hard one to expose, anyway.
But you got the focus right.
The warm colour temperature - now I only guess - possibly comes from two different light sources, too, outside/window light on the bright side and lamp light on the dark.
What I find weirdest about this photo is the clear division in those two vertical halves of bright and dark.