It is very, very uncommon to thrust a freshman QB into a situation like this, especially when you have two other options who are experienced, and are reportedly playing neck and neck with your true freshman. You should always ease a freshman QB into the college game as much as possible - it doesn't matter how highly they are ranked. If there is other experienced talent that can play, you should at least start that player in Game 1, and ease your true freshman into the experience.
Look at what Clemson did with Trevor Lawrence last year. Game 1, against an FCS opponent, they started their experienced QB over Lawrence, and have Lawrence limited playing time, which increased as the season went on. By halfway through the season, Swinney decided that Lawrence had fully settled in to college, and thus decided to start him. We are talking about a heisman level talent, but even he needed to be eased into the college game, simply because it's the right thing to do. Even if your true freshman QB is the best player in practice, you don't want inexperience to cost you games early in the season.
To me, this is a little alarming for UNC. I would much rather start Cade Fortin, who has the most experience, and let him at least play a drive or two, before I decide to put in a true freshman QB, especially in a game as big as this one. What UNC is deciding to do puts all the pressure on his shoulders, and he's never even experienced what being on a college field is even like. I would be concerned that this means the other QB's are really struggling, and Mack is worried that if he starts them over Howell, USC could take advantage early over some sloppy quarterback play.