Strange Ending to Seton Hall Win - ESPN Video - ESPN
This link is much clearer, and sound is better. You can almost hear someone calling for a timeout at the same time as the whistle blows. It also looks like everyone stops moving at that point. It also looks like Pitino is getting up to get his players together for a timeout.
I think the SH kid thought a timeout was called, stepped on the court to go to his bench, then realized play was still live. So he instinctively threw the ball to the ref, who seems to be asking for it.