Puzzler 3, to me, implies the author assumed both sides come to know of the state of a single duplex connection, rather than both having their own state of a simplex connection. TCP has always been designed to allow one side to continue receiving after indicating to the other side they are finished sending, and it requires both sides to close before the whole connection can end.
https://www.rfc-editor.org/rfc/rfc793#section-3.5