I don't see anything inherently wrong with your answer. Nor do I see a pattern of poor answers or down-voting on your content. Sometimes down-votes are just somewhat… random. An isolate vote in either direction is not typically something to worry about.
I understand that the occasional random (even undeserved) down-vote can sting a bit. But, as you use the system and gain a bit of reputation, accounting for each and every point becomes less of a concern and you can better enjoy the use of the site. Consider for a moment that, for every undeserved down-vote, you've probably also received the occasional up-vote you didn't deserve either. Remember:
- Up-vote = +10 points
- Down-vote = -2 points
And in meta, down-votes don't cost any reputation. If the vote was not random, someone was simply saying they do not agree with your suggestion. Nothing to worry about.