Then the answer is simple. Somehow, from your perspective, the main body of Inhumanity has yet to become public knowledge.

[ It would never occur to Medusa that Attilan would not exist. That is not how the laws of alternate universes work. She's no Reed Richards, but even she knows that. ]

Potentially you are a member of one of the lost tribes, the Inhuman diaspora following an ancient schism. Since we did not teach our children of them in Attilan, I doubt they ever taught their children about the kingdom they left behind. It would have been carefully guarded knowledge.