Because he was rude to you for no good reason. He hurt you with his indifference. That you are a big fan makes it hurt even worse. You've invested your emotions in him and he crapped on you.

I'd be curious to know who this was. My first reaction to his behavior is that he was under the influence of some substance, but that in no way excuses his rotten attitude toward someone who has helped him advance his career, you, the fan.