There were many rumors that were spurred on when the Colossal Wyvern attacked the City of Gloria and several other villages were attacked by numerous weyr of wyverns that all descended from the Endless Passes.
Many assumed that it was something even scarier than a colossal winged creature that made them flee from the mountains—maybe not a dragon—but something immense that made them migrate.
As to how the Colossal Wyvern arrived so fast however in the first place at City of Gloria was not lost to many that paid close attention to how the world operated and functioned. The secrets to teleportation was something already long gone from the civilization of humans—and wasn't recovered even when Han gained the scroll of grand teleportation.
