The way I understand it, it's not the meat that's sushi-grade. It's the way it's preserved / delivered. Basically if you can eat it raw and not let the parasites from salmon grow, then it's sushi-grade. Most commonly that means storing salmon in a freezer which kills the parasites. (think -50C)
Even if salmon wasn't traditionally consumed in sushi by the Japanese, wouldn't the later reversal indicate that, even in Japan, there is such a thing as sushi-grade salmon?
