The paper itself goes into detail about why the US Constitution and other memorized texts are misclassified. It’s surprising but not a killer flaw, since in most contexts it would only apply to direct quotes of famous texts.
It is what you get when you ask ChatGPT for the US constitution, so yeah, AI generated.
This effect is described in the article. And depending on the context, it can be a feature rather than a bug. If you are using an LLM detector to check if a news article or student essay is "legit", then not only you don't want something from a LLM, but you don't want copy-paste plagiarism either. So for the purpose of checking legitimacy of supposedly original work, then it is a desirable kind of false positive.
I suppose simpler techniques can then be use to check for verbatim copies of famous text.
I just added another tweet with the caveat others mentioned. (It was not an intentional omission)
It’s still not a nuance that most people trying to identify AI will respect even if they know it. Given that constraint, I really doubt the accuracy metrics as well.
Not very promising, though.