According to the GALE ENCYCLOPEDIA OF AMERICAN LAW, plagiarism is "The act of appropriating the literary composition of another author, or excerpts,
ideas, or passages therefrom, and passing the material off as one’s own creation." Black's Law Dictionary defines plagiarism as "the deliberate and knowing presentation of another person's original ideas or creative expressions as one's own," and goes on to point out when the act becomes criminal, i.e., illicit financial gain. I don't see that the author claimed ownership of the piece (literary or not)--and, in fact--identified it by name, give or take the missing article, or tried to make money from a loop. Given the first definition, sampling without giving credit to the original author is plagiarism...