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.
That’s what I mean though, terminally online mods ruin it for a lot of us. No way in hell do I have an hour or more a day to commit to policing others, yet there are mods on all social media that love to do it for free. When it’s free you get a selection bias for motive. Not dissimilar to real world police.