The mod banning these users is the same mod who made the posts they downvoted. This is mod abuse, turning the downvote button into an auto-self-ban button.
The message is “If you disagree with me, you will be banned”
Monitoring and banning users for using lemmy as intended to signal boost your opinion should be grounds to have all mod privileges removed. This behaviour undermines the integrity of the server and the wider fediverse.
In that case, this isn’t about mass downvoting, this is about users being banned by the moderator for downvoting one (1) post, one (1) time. The ‘mass downvoting’ (read, multiple users downvoting each post they don’t like one time each, as intended, and being banned for it) is my other post.