I'd be inclined to say it can't be the Giganticus Lupicus reference, since that's presented as prehistorical information. Counting that as "recorded history" would be equivalent to counting the last sixty five million years as "recorded history" because that's how long ago the dinosaurs died out.
Without that, the oldest record we know of was the arrival of the Forgotten, which means that the gods predate what recorded history we know. Now, it might turn out that Charr recorded history goes back further, but even they reference Melandru's involvement in the creation (terraforming?) of the world as a legend rather than as recorded history, so I'd say there's nothing that conclusively rules out a divine origin for the Cauldron.