Princess Kaguya and Rikudou's Tribe Became the Uzumaki Clan
Like I have said before, the Rikudou Sennin was born from a woman like any other human being, unlike other's assumption that he was a god who descended into the world without relatives:
Rikudou Sennin/Hagoromo Ootsuki's mother was a Princess:
A princess of what during ancient times? a tribe:
An Era when tribes worship Nature (Animism/Shamanism), which in this case is the God-Tree: The Juubi.
Kaguya and her tribe were probably the shamanic guardians (albeit non-ninjutsu wielders) of the God-Tree:
That is why she had direct knowledge and access to the tree and its fruit:
Like I've said, tribes/clans were already in existence even before the Shinobi Era:
I believe that when Rikudou/Hagoromo Ootsuki started the Shinobi Era, he converted his and his mother's tribe members and kindred into the modern Shinobi-Era Clan.
Which became the Uzumaki Clan:
It only proves Kushina's statement that the Uzumaki Clan were distant blood relatives, they descended not directly from Rikudou Sennin like the Senju and Uchiha but from Rikudou/Hagoromo's kindred
Some will insist that the Uzumaki Clan descended from the Younger Son only but this isn't true because the Younger Son's descendants were specified to have been the Senjus only:
And only during a later time that the Elder and Younger Son's descendants were called the Senjus and Uchihas.
It's just the same with the Elder and Younger Sons of Rikudou, the Elder was (First Name) Ootsuki while the Younger was (First Name) Ootsuki but their descendants became the Uchihas and Senjus, even if they weren't called Uchihas and Senjus, the Elder Son was an Uchiha because he was the Uchiha Ancestor while the Younger Son was the Senju Ancestor, same thing with the Uzumaki Clan: Hagoromo Ootsuki's Tribesmen/Kinsmen were the Progenitor Uzumakis making Rikudou and his kin the First Uzumakis.
I firmly believe that Princess Kaguya/Hagoromo's Tribe were the Progenitor Uzumakis aka the first Uzumakis, they may have had the surname Ootsutsuki, but most probably during the dawn of the New Era aka Shinobi Era their Tribe became the Uzumaki Tribe.
Which only makes sense for Rikudou/Hagoromo to reincarnate himself from his own tribe kindred: