The point is mostly so that anyone that comes from planet Yamatai is a "Yamataian". Whether they are human/civilian or nekovalkyrja. By the same by, a nekovalkyrja can claim she is Yamataian. Essentially part of the Yamataian people.
I don't see the change as abrupt, so much as something that makes sense and was adjusted because the word 'Yamataian' was already used in other context - and it had already been broadly discussed while I was working on the NH-30 (in fact, you can probably blame me for this - I'm fairly certain I'm the one that cared enough about this to make it an issue from the first). "Yamataian design", "Yamataian ship", "Yamataian food", etc... and all along we weren't referencing the NH-22C so much as the culture.
ICly, it's probably more an issue of the NH-22C having been misnamed, and the people at KZ eventually figuring out a Yamataian Yamataian was a bit confusing, since anyone from Yamatai is a Yamataian... so they wizened up and corrected that when chosing the name of the subsequent iteration.