Looking at stat rankings it may boil down to

[daj2576]

3rd down conversions. Since I haven't seen Indiana play and don't know anything about them I decided to look at my score app for the difference in matchup.
As solid as UT has been on 3rd downs (43%, ranked 33rd) Indiana is ranked 12th nationally at 48%.
Now, you may not be interested in Indiana's 31st ranked total offense, or the fact they're averaging 8 more points a game, citing how well UT's defense is playing. However, they are 5th in the country in TOP, holding the ball a solid 5 minutes longer than UT.
Also, while their defense doesn't rank as well as UT's, they're still only allowing 3 points per game more, which doesn't bode well for a Vols squad that struggles mightily in the redzone (also points to 3rd down conversions).
So someone who actually knows anything about Indiana football may come on here and say otherwise, but just glancing at those rankings I was surprised that another 8-4 team was pretty good at 3rd down conversions.
Edit: Indiana is 8-4

Stats against dissimilar opponents are not strong indicators of anything. What is a strong indicator, as I've said on here many times, is talent.

The team that recruits better wins considerably more than not. UT is considerably more talented than Indiana (17th most talented roster vs. 41st).

To put that in perspective, if Indiana was on UT's schedule they would fall between Missouri and Vanderbilt insofar as talent (they're the 8th most talented team we face this year); on their schedule we are the 4th most talented team (falling between Michigan and Nebraska). Tennessee is under-performing expectations by two games while Indiana is over performing expectations by two games. We've beaten 4 teams more talented than them. They've beaten no teams as talented as us.

Our best wins are against the 19, 22, 33, 38 and 57th rosters. Theirs come against the 20, 35, 47, 50 and 59th rosters. We lost games against the 75 and 106th ranked rosters, and Indiana is certainly more talented than either of those teams (so a loss isn't impossible, but that is true regardless of the BYU and GSU outcomes), but since those first two games UT has performed exactly as talent would predict.