Is it a PTB move ([email protected]) to ban a user if their only activity in a community is downvoting posts?

The behaviour baffles me a bit. If they dislike the majority of the posts in a community, why are they subscribed? Or if they are browsing by /all, why have they not blocked the community? Are they under the mistaken impression that Lemmy has an algorithm which uses downvotes as an indicator for “show me less of this”?

Has anyone else encountered a “serial downvoter” in any of their communities?