I just rewatched the end of the game, trying to see the play you were talking of.
According to the game log you posted, it has to be this one :
3:47 83-98 Leon Powe makes dunk (Paul Pierce assists)
Here is the play : Pierce's got the ball, LeBron is defending on him, then Pierce dribbles and Perkins sets a screen so Ilgauskas goes on Paul to stop him but he passes him by and LeBron is too late on the rotation (largely due to Perk's screen) so Pierce can drive to the paint, where he makes an easy pass to Powe, who dunks easily.
Just after this dunk, Z turns to LeBron (on top right of the court) and yells at him while clapping his hands with rage. Then we can see he keeps talking to LeBron but the camera sets on Pierce on the other side of the court and we don't see the scene. There are no replays of this action so that's all we can see! I'm impressed that you were able to see that during the game because it was a very brief scene but you are right, it's very funny (and unusual) to see that.
