If this is the reason of the ban then hilariousandco can easily unban him, but what if this is not the real cause of the ban!! hilariousandco should contact the one who banned the account for clarification.
Only theymos can see who banned him, but there's only one report on the queue on that user and it follows a few others banned for copy and pasting in the same thread.
Manually banning people is clunky and very time-consuming and we have a one click button for a permaban so that's what usually happens. The ban message should probably be chnaged to you have been banned for plagiarism since that's probably what it's used for in 99% of cases. I have requested an additional button that gives the same message to clear up further confusion.