There is no way that two individual guitarists would come up with the same iconic guitar part for an a cappella melody. It is not only implausible, it is impossible. The same hammer-ons and pull-offs and the chord shifts suggest one originator. That is why lyrics and arrangements are two separate credits on the same song. The fact that Jansch listed it as a Trad song does not take away from the gifted arrangement of the piece and one that was honed from playing it live. Such a captivating piece would prick up the ears of any guitarist. The fact that it appeared only as an instrumental from Page means that the arrangement contribution to a traditional piece by Jansch is most likely the case.