It's also possible that fans are blowing things out of proportion. Maybe it's just a case where a bunch of teenagers that had just gone on the road and drubbed Duke 48-0 the week before were feeling themselves because they were on a 5 game win streak, and they were lazy and unfocused in practice, which translated to an awful showing on the field. The players thought a home game against UNC wasn't going to be nearly as challenging as it turned out to be (the year before, UNC at home beat a 6 win UM team primarily because Miami's kicker got the yips and couldn't kick FGs). Unfortunately for Miami, Mack Brown had his team laser focused on Miami. Yeah, the game probably mattered a lot to Diaz, but I don't think players felt that same urgency (personally, I've never really considered UNC a major rival so I can understand that sentiment. I get a lot more invested when we play VT than when I play UNC). Miami players weren't focused, just like UNC players weren't focused earlier in the season an atrocious FSU- they thought it would a cakewalk and took a L. Things like motivation matter a lot with teenagers.
Would it surprise you to learn that VT actually had a better rushing offense than UNC last year? UNC was ranked #11, VT had the #10 rushing offense. VT was like a Paul Johnson GT offense from a few years back, pretty much their entire offense was the run game (the stats weirdly showed that whenever Hooker passed for more than 200 yards, it was basically a guaranteed L for VT). Miami managed to play disciplined defense (LBs were absolutely vital to keeping Hooker's damage to a minimum) and the defense contained their run game rather well.