To what degree are states allowed to regulate unmanned aircraft?

I’ve always understood that the FAA has sole authority over the airspace and how they regulate it. This seemed to be reinforced by Chicago and a few other cities/municipalities loosing court battles when they tried to regulate in certain ways. Now looking at the North Carolina DOT website, the state not only requires commercial operators to have their part 107, but to pass a separate knowledge test and then obtain a permit from the state. Does this overstep the FAA’s authority over the airspace, or are they operating within the confines of the law? Their website even acknowledges that the FAA has sole authority over the airspace in the United States, but then they go on to say “NCDOT has the authority to implement and manage regulations pertaining to state laws concerning drone operations within the state.” That seems to go directly against what the FAA says. Does anyone have some insight to if these laws are legitimate in the eyes if the FAA?TLDR; is North Carolina over stepping their bounds in trying to regulate UAS in the state? via /r/drones http://bit.ly/2DKU3SO