No, it's not plagiarism. Credit to the source is given in both the text and the list of references.
Yes, this is plagiarism. Joe Student did not use quotation marks.
This is not plagiarism. Quotation marks are used when citing someone's exact words. When you paraphrase, simply include an in-text citation or footnote. In this case, "(Zeil, 2005)" is enough to acknowledge the work of the other researcher.