PaperRater.com cannot tell the difference between plagiarism and an idiom

PaperRater.com claims to be a plagiarism checker that helps students avoid plagiarism claims but in reality, it is just a botched AI program. How can I say this? Well, my teacher asked our class to submit our papers via this website so that we can include the paper checker information for free when we submit our work. I noticed that it flagged a particular phrase, "Nothing could be further from the truth", as being plagiarized from a blog site. It asked me to properly reference the phrase to avoid plagiarism deductions. Huh? I mean, what? Since when did an idiom need to be referenced? Does that make sense to anybody here? I submitted my paper to my teacher without referencing that phrase and he did not seem to have any problem with it. So why did the program flag it then?

This is what I have been saying all these years. These plagiarism checkers are useless since the program cannot understand the eccentricities of languages as it is reviewed by the system. I would like to point out that PaperRater has been around far longer than AI. I was the precursor to AI checking technology and it has not done a good job at it. Why teachers continue to use this to make their jobs easier is beyond me. I miss the days when teachers actually cared about their jobs and took the time to read the student submissions and grade it based on merit rather than technical advice. I know that time is not going to be coming back anymore and the ones that lose because of the over dependence of education on technology, are the students.