Good day , community !

First of, I love askubuntu and the community here seems to be so much more friendlier than on other sites ! good job, admins ! As for meta , it's my first time asking a question here

I've a small question. On this answer I've downvoted new user's answer, which clearly doesn't add anything to solve the problem. At the same time, I've got -1 from my points. This happened once in past, too, but I've brushed it off since i was in a rush.

Could someone please explain why does this happen or point me to the appropriate post with this rule outlined (if it is a rule and not a glitch )?