PLEASE HELP! AN OFFER ME YOUR OPINION? IS THIS PERSON GUILTY OF PLAGIARISM? help..?

Joe, a student at Lester B Pearson CI, has a term paper due on Hamlet for his English cl. He decides to go to "Hamnotes", an online website which contains summaries of the plot, critical reviews and character sketches. Joe copies and pastes a quotation from a critical review into the text of his essay. He does not cite the original author. When confronted, he claims that this was unintentional and that he didn't know he was plagiarizing.