Bot retroactively banned a user for previous @everyone messages they had sent a long time ago when they had a staff role, but no longer has that role.
The channel was loaded after no one interacted with it for several months, and the bot somehow scanned the old messages as soon as a user loaded the channel and banned the previous staff user as if they were new messages?
I find this kind of behaviour from the bot to be a little odd, but I can understand why it occurred. Might want to add protections to prevent this from occurring to others in the future.