why was it mention that Kaguya came from a far away land only to then say that it was not important.
Probably to uphold the mysticism and other-worldliness surrounding her character. Naruto badgering Hagoromo for more information means that Kishi would be forced to try and explain how she could have existed in a celestial world beyond the confines of Earth (one that was alleged to have only been created after her son divided the Jubi's body into nine separate entities). The conversation would have been steered off-track so Kishi just decided to cut it short.