I actually had the same problem with a legitimate question that had no problem at all, apart from being more directed to new players. It got suddenly a negative vote without any explanation (frankly, I would be ok with a downvote if the person indicates to me what is wrong, because I certainly try to correct the information, even if the downvote stays there forever).
Honestly, I rarely use the downvote feature, since I think that making a thread negative is something worth only to "explicit" poor content. Overall if a question or answer isn't something that makes me care about that or if it is something really basic, I just ignore it.