Who or what is Korgon in the novel, Eaters of the Dead: The Manuscript of Ibn Fadlan?

When Ibn Fadlan first inquires about the nature of this beast he is told it is a fierce fire-breathing dragon. As such the warriors and the buildings are doused with water in the hopes of preventing everything from going up in flames. When the Glowworm Dragon Korgon finally makes its appearance, Ibn Fadlan sees it is not really a dragon at all. Instead the "dragon" is made up of men riding on horseback and carrying torches.