I'm curious why a question like this is even asked. How in any way would his belief if it's a choice to be gay (which its obviously not) affect his ability to run the country. I wish we could actually talk about the issues for once.
Answered your own question. As you said, it's obviously not a choice. So if he answers an obvious question wrong, he's obviously a dullard and not fit to be president.
I strongly disagree, just because he doesn't know the facts to answer a random question like this does not disqualify him for the presidency. He has a great list of accomplishments as Governor of Wisconsin that surely make him fit to be president. The people that say this disqualifies him from the presidency weren't voting for him anyway, luckily I don't think the majority of people would change a vote based on something as silly as this comment.