From that video it looks like Pierce and Paul were talking and ROndo came over and said something and started pushing Paul. Bottom line, who cares?
I don't know the first very few seconds of the tape show Paul saying something none to nice to Pierce. It didn't look like what he was saying to Pierce was the usual:
"Hey man, great game. You guys got a hell of a team. By the way, what you doing after the game? We aren't flying out until tomorrow so come by the Copley Plaza and pick me up and we'll go hit the Capital Grille for some steaks."
Pierce's facial expression, for the very brief read I could get off it, looked more like a:
"Hey, go take up that crap with him. I'm the captain not a freaking baby sitter."
And then Rondo might have heard what Paul said and came over to see what was up.