Cheetah bot is warning people that their post has been flagged and the username put on a blacklist. Proving otherwise is great the ounce of prevention is way better.
Here proving that you never intended plagiarism could be done by both removing the stolen material or crediting it properly and enrolling in the classes that teach how not to plagiarize.
This of course would also mean learning how to find plagiarism and is a form of community service for the communities effort to educate. lol
"Perhaps as well add into terms and conditions, 'original content'." I think this is another great idea. Using terms and conditions to get consent.