If you are going to give feedback to a new user a downvote may not be clear, and I would go as far to say, is never clear. Please leave them a comment and explain the site, you can flag as Not an answer for a moderator or higher rep users to clear out the post with a delete and have a comment explain what they have misunderstood.
A good comment to leave might be along the lines of:
This forum is not like other forums, there is already an answer for
this question and the way to support it is up voting. The reason you
cannot upvote is because you have not yet attained the reputation
required to do so, a rough estimate of both expertise and knowledge of
the site. Please try to add new answers other places or ask questions
you have. If you have any confusion about the site, visit the