Esta passagem não é um fato histórico. Em vez disso, é algo que é dito a Lorgar para levá-lo mais longe no caminho para o Caos.
Não conheço nenhuma evidência que sugira que Khorne, Slannesh, Tezench ou Nurgle tenham sido mortais.
Depois de algumas pesquisas, descobri o seguinte:
O autor, o próprio ADB, afirma (no link ) :
It's a parable, about 4 travellers leaving Colchis and finding some vague truth / travelling to that region of space before it was the Eye / a reference to how Colchisians have always been pilgrims / a reference to how Chaos is eternal / a suggestion that a Chaos presence was always in that region of space to some degree and that humanity has forever been drawn to it / a way of suggesting to the Colchisian characters in the novel that their homeworld has always been chosen and inspired by Chaos.
It's not saying anything specific, and for the record, nor is it a retcon. It's a throwaway line about a legend. It's impossible that it could ever make sense. So obviously, it doesn't. Just a Colchisian version of the Odyssey, or the Bible, or the Mahabarat.