Keep in mind that Vegas isn't actually predicting the outcome of the game. Here's a helpful explanation on point spreads from wikipedia.
The point spread can be moved to any level to create an equal number of participants on each side of the wager. This allows a bookmaker to act as a market maker by accepting wagers on both sides of the spread. The bookmaker charges a commission, or vigorish, and acts as the counterparty for each participant. As long as the total amount wagered on each side is roughly equal, the bookmaker is unconcerned with the actual outcome; profits instead come from the commissions.
So with games like this, Vegas is playing more to perception than actual prediction. There's a lot of little things that make Vols fans more confident, and for good reason e.g The fact that these two teams are composed of the players who participated in last year's games which went pretty well for UT, Florida's history in Knoxville, how Tennessee is "hot" right now. But those things won't necessarily be considered by a lot of bettors nationally, who are probably looking at the stat predictors such as kenpom and Sagarin giving Florida an 80 percent chance with a line around where Vegas set it.