Indiana wasn’t a lock going into the weekend for several reasons, the biggest being the Texas-Texas A&M game.
The committee has already hinted that they do not plan to weigh a conference championship loss as heavily as they did a regular season loss. So, if A&M had beaten Texas and made it into the SEC championship game, they were likely going to be a 4th SEC team in the field, and Indiana was most at risk of losing their spot if that happened.
With the A&M loss they are basically in and the last spot comes down to SMU if they lose, Miami, and three 3 loss SEC teams.