It is up to you on how you would like the finish to look. I usually ask my clients and explain the differences in finishes that can be achieved and how they vary in appearance. Some like the look of a hand done door using a brush and having slight signs of the door being done by hand rather being done using equipment. There are ways to do a door by using hand tools and not spraying to have a door look like it was sprayed. But to your question, the particulars should have been discussed before hand. Ask your painter if he is able to sand out some of the brush marks and redo the door either by hand or spray but that you want a sprayed like finish rather than brush marks. Do you have pictures of the door?

If the painter used a latex paint on the door, good luck trying to sand out the brush marks. Stripping would be required to totally get rid of them.

Rather than stripping it i would skim coat out the whole door if it bothers you that much or looks that bad. It's much faster, easier, less mess, and nothing will be wrecked or ruined from the harsh chemicals in stripper.