I'd like to add a few things to what commando already has mentioned.
Either the site has a mutable set of rules or guides, and I haven't been made aware of them, or the majority of regular users are voting based on their personal perferences -- likely for the person who is posting.
Yes, the rules are mutable (that's what we do here on meta), but that's more of a long-term process. Yes, the majority of regular users is voting based on their personal preferences. Voting is inherently personal and designed to be so. That's why it's a privilege, gained at a certain reputation level: you are trusted to know enough about the site to have an idea about what good posts are, but this "good" is not defined and voters are not machines following a set of predefined rules. However, without e.g. comments indicating personal grudges it would be jumping to conclusions to claim that the sole reasons for votes is the post's author.
That being said, your post has only received one downvote, which I think is negligible. Also, do you remember when you received that downvote? If it was on the first revision of your post, that would be understandable, wouldn't it? Anyway, don't worry about it. Everybody receives sporadic downvotes. When your posts are getting downvoted systematically, there is a detection system in place which will notify the moderators.