Excellent observation and explanation. Yes, Nole surely comes across to the crowd as arrogant, being only an extreme extrovert, born and raised in another type of culture that does not insist on the stiff upper lip conduct. I am very much aware of that --- he needn't do anything apart from simply showing and expressing his true feelings strongly, and, there you go, he's taken to be as chesty as a peacock. Which is completely wrong because he's only a very intelligent youngster, even overly serious and considerate of other people's opinions (at least from what I saw in a couple of TV interviews). That's why I think you were spot on.
quite strange though, because that's not a phrase I would use to describe Nadal -- especially not on court with the raised leg, fist pump VAMOS, etc. Maybe people think Spaniards are more 'allowed' to be fiery, with their flamenco music and bullfighting. Maybe they are more judgmental about other cultures being passionate.