Although I think that people should not behave like this, I disagree that it is "unprofessional", "unbelievable", or "wrong". In fact, I argue that nothing is more professional than doing whatever you can to get an edge to win the game. His attitude may have thrown his opponents off their game, make them lose confidence, etc. Sure, EG probably didn't need it, but the behaviour is professional and what I want my prize fighter or lawyer to do if it will give them an advantage within the rules.
As for unbelievable, if you were familiar at all with PPD then you should believe it. Dota 2 is a game played by kids, and in EG's case, kids with a lot of money. Do you know why a lot of troubled sportspeople come from basketball? It's because they're given a lot of fame and money before they know what to do with it and handle it. Judge them harshly if you will, but remember they don't have agents, and eSports is still relatively new. There is also no overarching governing body (NBA, NFL, etc.) that will put their career at risk. On top of that, was this a private conversation? Because the only difference between this and what goes on on the field of a real sport is that this was recorded and posted publicly. I have heard many tales of superstars asking bench players, "Who are you?" and even worse. You may argue that that's not necessary, but we ask them to be competitive monsters and have that killer edge. Sometimes you see the monster.
So, what I'm trying to say is, if you're taking eSports seriously, and you want players to take eSports seriously, then professionalism isn't defined like it is for an office worker. To me, it is defined as "wanting to win", and every team and player should push the limit of that as far as they can (legally), EternalEnvy style.
Finally, regarding the fact that there is a rule regarding respecting other players, it's not like a racial slur or homophobic slur was used here. He commented on their abilities as players, and that's fair game as far I'm concerned. The rule is there so that they have something to refer to when people get out of hand, but that's not what happened here.
If you want more of my viewpoint, I actually blogged about it: http://ganktheplanet.blogspot.ca/2015/03/the-esports-trash-talk-dilemma.html