AD and him butted heads. Garcia (AD at the time) didn’t like the fact that Cristobal was getting all the credit for bringing success to a once trash program (he won a school-record 8 games the year before he was fired, seven before that). Cristobal wanted more commitment to facilities and the program in return for winning more games.
In fact I remember hearing that Garcia was actively trying to push Mario away to Rutgers after he went 8-5 and his name was swirling out there.
After going 3-9 the following season, Garcia swiftly took his chance to fire him and seize control.
With that being said, they were picked to finish at the top of the conference and absolutely disappointed. But the hatred between Coach and AD was set in stone before that.