The answer was down voted because I lost my keys. Please, stay with me, let me explain this odd chain of events.
Earlier today I couldn't get to the store on time because I could not find my keys. That caused me to miss the opportunity to run over a golf ball, which would have bounced between a few buildings in Makati and eventually land in one of the fish ponds at the park.
If that had happened, a fish would have been frightened, and not swum over to distract a little girl. But since the girl was distracted by the fish, she didn't stay with her dad on the way back to the car, and he left without her.
When he got home, he realized that he forgot something, but because the kid wasn't there the cat didn't hide so the guy tripped over the cat — and into his desk where he went to catch his balance.
While trying to get his balance, he accidentally clicked his mouse while the pointer was hovering over the down-vote button on your answer.
Now, because he was in such a hurry to get back to the park, he missed the grace period where he could have taken the vote back (had he even realized his mistake, which I doubt, he was in a bit of a panic at the time).
So you see, it's my fault that your answer was down voted, and I'm dreadfully sorry about that. I'll try to stop misplacing my keys, but I can't guarantee anything.
On a more serious note, some have attributed this to various phases of the moon. Sometimes, well, people just do odd things. It's one down vote, don't worry about it - as long as you're sure that your answer is good, then put it out of mind. The amount of entropy involved in a site of this scale is just too much to even hope for any kind of accuracy in a guess as to why it happened.
The real question remains, though, which is where the heck are my keys? I still haven't found them.