UNC's expected defensive performance against Notre Dame should have yielded 100.2 points / 100 possessions. Instead, they allowed 119.8 points / 100 possessions. This is a factor for why UNC's defense is as low (12th) as it is. The problem was, UNC didn't play defense simply because they didn't have to! If your offense has a very good day, and you are up by 20 or 30, there isn't a great need for playing your best defense. While this isn't smart when you're up 5 or 10, when you're up 20 or 30, teams can play more relaxed (reducing injuries) and can allow bench-players to have more time (giving them experience).
As it just so happens, UNC was having an insane offensive day: 140.5 points per 100 possessions! UNC began dominating Notre Dame by being up about 18 or so. At one point, the margin got down to 11 or so, but UNC answered with an 'offense-for-defense' and boosted their margin more. What does this tell us:
In perhaps a small amount, UNC's offense is as overrated as their defense is underrated. A better representation of a team's performance would be their efficiency margin. Carolina was probably predicted to win by about 10 points per 100 possessions, when in actuality they won by around 20 points per 100 possessions.
As long as the teams' efficiency margins are adjusted for strength-of-schedule, I think this would be a better rating system than kenpom's, as it involves what goes through the players' and coaches' heads. Scoring margin, as we have discussed, is a false indicator of team-matchup winners, and therefore would work less.