well sometimes there is no way to control one's emotions as they may overflow and overwhelm you.
just guessing here as I am not really all that emotional on the average. but that is just me.
pete held so much inside that maybe he could not hold it anymore.
anyway I would have to agree about fed and pete on grass:
pete was too strong mentally and his serve was nearly unbreakable. he would have held his own against fed's weaker wing with his serve.
a decisive edge would have gone to pete in the tiebreakers on grass.
pete was also very sure of himself at the net. very confident and very adept at the net. so a slight edge to pete going forward.
lets say they are both at their peak on grass and they play 7 matches. and the grass is relatively fast:
I would have to give pete 5 matches and Federer 2.