Consequence of lack of onboarding. Would be easily fixed by popping up instructions for voting and feed shaping the first time a new user votes.
Quora may be exacerbating the behaviour by automatically blocking topics when you downvote questions. They also downvote a question for you when you only want to report it for something. The downvote remains after the reported issue has been corrected.
Cryptic mess, needs a redesign.