The last of the Nomai, a girl named Quartz who founded the Secret Library, is killed by Loki.
This genocide was done for 2 reasons. Firstly, Odin wanted to do it. In his eyes, the nomai standing against them was the same as standing WITH the dragons, so he wanted them all gone.
Secondly, the Nomai still possessed technology that posed a massive threat to the Yorkeluns’ control of the world. In order to maintain absolute power, they were wiped out, with the general public believing that they were defeated in the war – as everyone still thought the Nomai were fighting in the war.
This is different than how they covered up the dragonborn genocide, as nobody knew of the dragonborn’s existence, so they had much less to cover up.