Hi Max,
I have taken a look in this and I can confirm the fact what you have seen. That one particular user has given you a very bad vote and then given another extensions a very favourable vote. Since both you and the other extension have so far very few votes, it makes a difference.
However, every user is free to place their votes at their own discretion, as long the users aren't voting systematic on extensions they haven't tried. The idea with the votes is to give the user a way to give one's opinion on an extension. However people have different grade scopes and valuable different things.
Unfortunately, what you have seen is quite common, when a user isn't happy with an extension, they give it 1 and when they think it's a good extension, they give it a 5 and the scales between don't exist for them. It isn't much we can do about it, more than encogurage the users to vote with responsibility.
In your case, this partical vote will reduce in signification when you get more votes. I think the people read the reviews and look at the totality, and not to an occasional bad vote. Sometimes you as developer, will get a bad vote or review and if it's a review, then you can always use the owners reply function and try to explain the critics in a responsible way or try to give a good feedback to it. Then the users see that you are a responsible developer and that you care about the critics and your extension in a good way and I think this is much more important than just some ocassional bad votes / reviews.
Good luck
