A computer will correctly score that b as a dead stone, since it can't possibly make life, and white can kill it. That insurmountable threat makes the territory white's.

If a human tries to argue that b is alive, then either (a) that human is a novice, you can teach them, or (b) that human is a poor sport, and you shouldn't play with them.

Japanese counting is like Chinese counting, but assumes your opponent is not a jerk without explicitly handling cases when that's not true.