I mean... there are a lot of possibilities here. It's really not all that confusing/lore-contradicting when you think about it. The mother could have left the main tribe, as many Seekers do, to live outside the tribe's traditional restrictions and taken her son with her, then had a daughter later by someone who wasn't the Nunh. Speaking of, I'm sure many Nunh's aren't exactly "father figures" (especially not in the traditional sense) given their status as the "breeding male" of the tribe; even if they grew up with the tribe, there's still that issue.

This guy was an event character, and a thus far non-recurring one at that. I don't anticipate them writing a detailed backstory for a character like that in the first place. I do not think they totally ignored lore here though; there are plenty of possibilities that make this scenario work if you just use a bit of imagination. :P