It is common for a painter to utilize available space in a new home or building for finishing woodwork and the like. I have done this myself and I also have my own building I use as a spray booth.
It would have been nice if the painter took greater care to cover things better. It is their responsibility to make sure all items are clean and in proper working order. I'm sure they plan on repainting the walls and ceiling in this room. The concrete floor shouldn't be a problem when the carpet is installed.
Make sure the painter puts the room back into proper order. Voice your concerns, I'm sure the painter is interested in providing quality workmanship and would like you to be happy. A happy customer is a "recommending" customer.