You don't have to be Japanese to know how to make sushi or other Japanese dishes properly.
That may be so, however the broth they use for their ramen and udon is NOT authentic Japanese flavors, neither are some of their other dishes. It has a Korean flavor to it. Same goes for the "Chinese" restuarants in the area. Because of the dislike by the Americans for real/authentic Chinese food, the flavors have changed so much that you almost always have to drive to South Sac or the Bay Area to get the more authentic type of cooking.
And since I don't know much about Mexican food, I don't know what is considered to be authentic of not. But I do know my differences in authentic Chinese and Japanese cooking, and Japanese food w/ a Korean flavor is NOT authentic.
That being said, I do still think Naniha has some good food and they also offer some Japanese dishes that I haven't seen in other restuarants. But there is the Korean influence on the flavor, just like Kirala has a Chinese influence on the flavor.
As for eating sushi, it's hard to mess up the flavor of the fish, and whatever you make the rolls out if, it will have that flavor.