For what it's worth, "secret names" (which are also sometimes a "true" name, in a metaphysical sense) are pretty common in fantasy and myth, and I wouldn't be surprised if that was worked into Earwa's worldbuilding. That being said I'm not sure how much legit evidence there actually is for it at the moment, and I wouldn't necessarily link that Nonman line with the concept.
At the same time it totally could be. Particularly since such a thing would more than likely apply to Kellhus anyway. For example, in a lot of myths, there would be a notion of an extremely powerful deity who could only be killed/defeated by knowing their "secret name". And then, of course, there are a million and one riffs on that concept itself, so who knows.