Right, he was referring to the WoL being the 'Eikon Slayer' that eats Primals for breakfast (as far as the Garleans believe), and yes, that includes Bahamut. Information about the player's exploits were being constantly funnelled back to Garlemald through Zenos's forces in Ala Mhigo by Eorzean spies like Roalie, so he knows everything we've done, including our very lofty reputation.