I am not getting rewards or anything so I don't think that is the case. I don't know why its spam or plagiarism...and I actually like to know the reason.
I don't think upvote and downvote are the same...I have 5 upvotes and 2 downvotes on one post. But the post is still hidden and my reputation points still got destroyed...but then, I don't know exactly how this works so...¯_(ツ)_/¯