He didn’t leave Pitt for Nebraska. It was already announced that he wasn’t being retained at Pitt prior to him coming to Nebraska.
Report: Mark Whipple Met With Nebraska Sunday
Pitt offensive coordinator Mark Whipple interviewed with Nebraska Sunday, Parker Gabriel of the Lincoln Journal Star reported. This comes as Whipple reportedly resigned from Pitt Tuesday afternoon and will not coach in the Peach Bowl at the end of the month. Gabriel reported that Nebraska head...
pittsburghsportsnow.com
According to this he had net with Nebraska two days (Sunday, December 5th), prior to resigning on Tuesday, December 7th.
There was speculation that he wasn't going to return prior to this.
Both Whipple and Narduzzi have strong personalities. That's no secret. I imagine they bumped heads a few too many times.