Yes, I think we can say the fan's behavior and Artest's behavior was equally "professional."
I wouldn't say equally. The beer was thrown first --- that's how the whole thing got started --- the "fan" did it exactly to provoke a reaction. The players are being paid money to play a game --- not to have beer and chairs thrown at them. Honestly --- if someone you had no quarrel with just came up and threw something at you, would you have no reaction at all? You would just meekly stand there and take it?