Seems like he must be a worldhopper or perhaps, just a Shadesmar-hopper? We see the clear Selish connection, but he also has either been to, or knows of, Nalthis. When he says, "What Heightening are you?", it seems to be a reference to Awakeners seen in Warbreaker. This guy definitely knows his stuff! I hope we see him again in the future (or maybe he'll see us there)!