It's always highly recommended to reference any other places where you published your content before. Steemit is full of plagiarism which is why cheetah and steemcleaners exist.

I recommend joining steemit.chat and then the #steemcleaners-public channel so you can find out how to best confirm your ownership of the article on that other site. If you do that, cheetah's comment will be changed and you shouldn't run into the same problem again.

The danger of not confirming your identity is that you might get blacklisted ans automatically flagged.