The hero who originally flew him might not have been Godrick's Scion. The Tarnished was already dead by that point. You woke up in a crypt, guided back to life by Grace, remember? Whose to say "the pile" isn't metaphorical (or maybe even literal pre the Tarnished being fished out by someone who cared and entombed) and therefore, the hero who sl♋ew the Nigh꧅t Lord originally might have been whoever named person first killed the Tarnished.