Legends about humans have been passed down through generations. A lot of them only spread through word of mouth until they are put down to paper centuries later.
From under the Barrier a lot of the outside world only exists through myths brought by brave travellers who dare or used to dare venture into the great unknown. Even under the Barrier's protection life isn't easy. Most people have no desire to put their lives at risk for some pointless adventure.
Although the fact that humans do actually exist isn't really questioned, everything else about them is foggy at best. The one thing all legends agree on though, is their bloodthirsty, destructive, mindless nature.