I don’t think the guy meant to come in and stir up trouble. I don’t think the owner meant to defraud anyone. I think there was definitely some room for misunderstanding in the “all you can eat”. I would have called this a tie, until the lawsuit happened - that tips my opinion against the plaintiff.
You’re using a loophole and you know it.
It’s recognizable on the face of it that an “all you can eat” sushi restaurant is balancing off the high value of the expensive fish against the inexpensive nature of the rice. Everyone recognizes that, which is why they understand they have to eat the rice as well.
No “all you can eat” sashimi restaurant could stay in business for more than a day unless they charged a $100, and maybe not even then.
I strongly suspect that this jerk has played the same sneaky game at similar places and has gotten away with it by whipping out the “diabetic” card. I think Mr. Oh deserves support for calling him on it.