I'm curious about the Greystone thing as well (it really threw me for a loop when I saw it after waking up at 5am this morning and has been nagging me all through class).

I like the ASoFaI naming convention similarity idea, because if the name came from his mother, then that begs the question: why does it look so hyuran? Does Haurchefant harbor hyruan heritage that doesn't show AT ALL in his appearance? lol (I laugh but I would not put it past the devs)

And considering the racial divide which favors elezen in Ishgard, if they do give ll illegitimate children a generic last name (like in ASoFaI), I can see it making sense for the illegitimate-kid name to be of the hyuran convention.