The downvoting functionality here and in other forums can mean many things. It isn't a precise thing. If it is precise I'm not finding a clear definition. It can mean I disagree, this is boring, this is false, this made me sad, I don't like reading this, I don't like this user, I'm tired, etc.

One plausible interpretation of a downvote without a comment is drive-by snark without rationalizing.