I think they were just trying to generate action on the line – if they opened with Utah giving points, there wouldn’t have been that big push you saw to move the line in Utah’s favor.
Vegas almost always gets it wrong with the Utes, IMHO, because of a multitude of factors. First, Utah (in the past – hopefully this is changing) will never cover a big spread – regardless if it’s in our favor or not. We just don’t play blowout games, in either direction. So, I’ve made money taking Utah and the points, but learned to steer clear of giving 10 or more points to anyone, the most recent cover on the ND game, notwithstanding. Second, Utah is not a traditional football powerhouse, plays out west, and is not ‘flashy’ in its game plan (again, maybe this is changing?) – all of which means Utah garners very little attention from anyone not directly affected by the outcome of the games, e.g., only fans of the Pac12 or people who live in/have ties to the state of Utah really pay any attention to Utah football. Finally, a very large subset (majority?) of Utah fans do not gamble. So, the only way for oddsmakers to generate traffic on a Utah/BYU line is to make betting so enticing (getting points with Utah? Yes, please) that even the casual bettor will want in on the action.
My two cents, FWIW