The only upvoting or downvoting that is improper is voting that targets a specific user. Other than that, people may vote as they choose. So yes, if someone had downvoted your question, it would have been fine.
Furthermore, off-topic questions are good examples of the sort of thing that is reasonable to downvote. Remember, the vote is about the post, not about you personally. Neither the on-hold status of your post, nor votes on the post, necessarily mean you shouldn't have posted it originally. Your post turned out to be off-topic because it turned out to be a bug; at the time you posted it, it made sense to do so. It was not wrong for you to have posted it; neither on-hold status nor voting is generally a way of judging people.
As I am writing this, your on-hold question has one downvote. (The vote total expands to one upvote and one downvote.) As Oli eluded to, when a question is put on-hold as off-topic, the system downvotes the question. (This is not the case for all close reasons, but is the case for the off-topic close reason.) Therefore, no actual user of Ask Ubuntu downvoted your question.
As a concluding thought: The fact that the system automatically downvotes questions that are put on hold as off-topic makes it pretty clear that the designers of this system think it is acceptable to downvote any off-topic question.