Looks to me like Nebraska guy is looking to make the "LeBron-like" block from behind and is getting ready to swing his arm to block, but Davis throws the ball up earlier than he expected because Davis was losing his balance so it ends up no ball to block. In the under the basket camera angle you can almost see the Nebraska guy try to stop his arm but it is too late. Bad miscalculation by the Nebraska player, definitely his fault, but I do not think it was meant as a dirty play.
I'd say flagrant one, but not sure it warrants ejection.
That said, I also think a compounding factor not mentioned much is that the ref called the foul on the earlier trip, so Nebraska guy should have stopped and not even made a play at the ball, which came 2-3 steps after the whistle blew. The flagrant contact comes well after the initial whistle blew. That may have played a part in the reasoning for the ejection, too.
