If the point is to prove that the model contains an encoded version of the original article, and you make the model spit out the entire thing by just giving it the first paragraph or two, I don't see anything wrong with such a proof.
Your previous comment was suggesting that the entire article (or most of it) was included in the prompt/context, and that the part generated purely by the model was somehow generic enough that it could have feasibly been created without having an encoded/compressed/whatever version of the entire article somewhere.
Which does not appear to be the case.
That seems like a silly argument to me. A bit like claiming a piracy site is not responsible for hosting an unlicensed movie because you have to search for the movie to find it there.
(Or to be more precise, where you would have to upload a few seconds of the movie's trailer to get the whole movie.)