Most instances of hacking rely on social engineering because the human element is typically the weakest point of any system. Real life isn’t a movie, hacking is a hell of a lot more mundane and the ways hackers achieve their goals are often as silly as this case where someone literally left a door open. So yes, this sign was “hacked.” And yes, it was the result of a very stupid mistake on the part of an employee of the NCDOT. The term isn’t dependent on the difficulty or complexity of the task. It just refers to finding a vulnerability and exploiting it.