No, being a jerk is going about it the wrong way. This man is anything but humble. No one but small children believe in Santa and you can believe in Santa as a child and still be taught the lessons of Jesus that will last your whole life. To stick up for this guy is wrong-headed, let children believe in the "magic" of Santa Claus for a few years of their life. Relax
By taking out a bill board, he was making it hard on parents, upsetting little children, and calling attention to himself (he did get his name in the paper, didn't he?).
Regardless of the rightness (or, wrongness, in my opinion) his methods are what are objectionable. I would point out that while small children may on occasion be disillusioned by discovering that Santa is a myth, a whole lot of people are going to form the opinion that Christians are miserable fanaticts who haven't an ounce of fun in their being. Not a very good missionary tactic, in my opinion.