No wonder he doesn't remember it if it's 5 months ago... It seems a bit strange if it's not spotted for 5 months and they get to gain merit and activity and waste time doing it in the process... Although, plagiarism is plagiarism unless he can prove he owns that Twitter account or got permission to copy their messages (and the recent posts might have been deleted)...
A ban is a bit of an overkill in this situation. He should have posted with a source but in this case it looks like the user has been trying to be helpful rather than gaining activity on their account by copy and pasting. This is probably the first time I have seen someone plagiarize and feel sorry for them that they got banned.