Alternate angle shows that, after the buzzer sounded, Devin Booker walked over to the Clippers bench to taunt/gloat. The shove by Cousins followed shortly after:

Clippers and Bally Sports finalize new multi year broadcast deal

DeMarcus Cousins Absolutely Dominating In 3x3 Basketball

Devin Booker Post-Game, Im A Big Brooklyn Nets Fan, Call My Guy Tyler Johnson Making Sure Theyre Gonna Give It Their All

Trae Young beats the buzzer...almost