Board Thread:Episode Discussions/@comment-25319479-20160630125952/@comment-5407586-20160705190215

Black Zetsu states that the Six Paths — Chibaku Tensei was used to turn the Ten-Tails into the gravity core of the Moon. The Ten-Tails, not Kaguya. And Hagoromo didn't know about the Ten-Tails being a manifestation of Kaguya's will. Read chapter #681 for more details.