The term would actually be "Rebirth" (Buddhism) not "Reincarnation" (which is a Hindu belief) the Soul of Naruto is indeed that of Rikudou, but this is not a case of Soul Transmigration because Buddhism does not believe in a permanent self (Anatta) the rebirthed soul (Naruto) retains the karmic imprints of its previous life (Rikudou) but the memories, personality and identity of the previous (Rikudou) is not necessarily the same as the current (Naruto) so they are the same, and not the same being at the same time.
