Origin Question

So I know that the Leagues of Votann are a recon of the Squats from way back. But how do they explain the disappearance? And were the Squats also the cloned Votann but no one outside of them knew of the word Votann? Or am I way off and the Squats were something else entirely and devoured by Tyranids? (Forgive me, I'm still pretty new and splitting my time between Votann and Space Wolf lore so I may be missing things.)