Last season under current UNC defensive coordinator Everett Withers Minnesota was 119th(dead last) in the NCAA in total defense giving up an average of 518 yards per game. This season without Withers Minnesota improved to 75th in total defense giving up 378.4 yards per game.
Last season, UNC with Chuck Pagano running the defense was 35th in total defense giving up 349 yards per game. This season with Withers at defensive coordinator was 62nd in total defense giving up 357 yards per game.
The explanation given for Minnesota's defense being so bad was a lack of quality personnel. I think we can assume the personnel did not change all that much yet Minnesota's defense vastly improved without Withers. UNC on the other hand ended up being eight yards worse per game despite returning most of the starters and generally having enough quality talent.
It is quite possible the numbers mean nothing but more than UNC's increase in yards per game surrendered I find the improvement of Minnesota post-Withers to be somewhat shocking. The question is whether it is telling or not.