Burden of proof does rest on the person making the claim.
He's right though, there is backstory connecting him with Aspidis.
Given that the war in the South looks like it'll be winding down (either after a battle or after a surrender), The Council once again gives consideration to the North. Ships are sent to begin construction of a settlement on the coast West of where Avalonia (correctly) believes the Eastern Kingdoms to be, right in that bay there (Avalonia knows that it's just Erinaum now, because we've talked with Aspidis in the last two hundred years, but Avalonians still call it that) much like the one that Avalonia maintains farther North on the same coast (just where the coast begins to turn almost directly East). Aware that it would be impossible to maintain a large area of land up there, special efforts are made to make the locals like us and make sure that they'll support construction of a settlement, support construction of a road, and be better neighbors than those in the Pachtland have been.