Was it stupid? Sure. I don't feel bad for the guy over the negative attention he is getting.
Should the guy have to pay a $500,000 fine? No. Disproportionate punishment is wrong no matter what the circumstances.
What if it was just some 65 year old duffer who had a few too many beers in him and nailed the bird on purpose? Even if it was just a lucky one in a million shot, would he be fined $500k too? Doubt it. In fact, you never would have heard about it.