You can tell by looking at the color.

If it is the kind of mustard that is strong when squeezed a little, the color is particularly green and has no powdery texture. This kind of mustard is not ground from plant mustard, it feels like synthetic.

Generally, Japanese restaurants opened by Japanese in Shanghai or "Genroku conveyor belt sushi" use plant-ground wasabi.

So there is not only one store in Shanghai.