THIS is overzealous and is EXACTLY why ONLY the copyright owner is allowed to assert a (legal) claim of copyright violation.

On the one hand, I love the ability to find (likely) violations via search engines and plagiarism checkers. On the OTHER hand - they all suck in terms of their understanding of the law, and used by amateur sleuths and vigilantes, can do more harm than good.

I hate that a student's entire reputation might be tarnished by careless use of such checkers. My own kids were so paranoid about this that they would run their OWN WORK, which they knew to BE their own work, through no fewer than three different checkers, just to be sure no professors would dismiss them and punish them with "academic dishonesty" without a second thought.

I once reported to a fellow poet that I THOUGHT her work had been stolen online. She had used a pseudonym. I asked her - using one account and email address - to reply to me using the OTHER account and email address. That, in hindsight, may have been overzealous, but she understood and was appreciative of my diligence in letting her know that someone MIGHT have stolen her poem (she'd posted very slightly different versions on the two sites). But this was a good reminder of why third parties have no standing to press charges or bring suits or write DMCA take-down notices. We cannot always trust that they have good intentions or have done the due diligence.