We know less about Notch then we think. If he is related (son or brother) to Herobrine, chances are that he has a speck of evil inside him. But as I said, interpret it as you like.
Remember, this is Herobrine's perspective. He could be lying. He could be telling the truth and the brother story was a lie. The point is that you interpret it how you want.
I love different opinions. Makes it more interesting. I guess you're right, but considering the amount of Flame-Wars going on between the two, I decided to do this.