Answer: C. This is not plagiarism
Explanation: Plagiarism is the use of someone elses words or ideas as though they were your own.
Going through the student's write up, there was neither a word for word nor a paraphrasing plagiarism and at a point where he or she borrowed few words from the original content, the student enclosed them in a quotation mark so we can differenciate borrowed words from his or her own words. But the student made a mistake in the citation part, by wrongly citing a different author.
So that is not Plagiarism but if it were an assignment, a mark will be deducted for the mistake.