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The account was possibly banned after certain practices were highlighted
here and
here. I figure more posts were either reported or inspected in order to determine the final outcome (plagiarism is easy to prove, use of AI will likely take a bit more research in order to be able to conclude with enough confidence of not crossing a false positive).
I think his case might have something to do with him being banned for plagiarism before. He got a second chance after his
ban appeal in 2019. It is possible that the moderators have records or check the logs of such cases so they issued the permaban without much hesitation.