Exactly this. It's a dogwhistle for extreme anti-semites, whether the people sharing it know it or not.

Assuming you are correct, does that mean it should be impossible to criticize Soros? A group of radicals dislike him, therefore he is beyond reproach?

There's a pretty big gulf between disliking someone and spreading inane anti-Semitic conspiracy theories. Most of the "criticisms" I see of him are very much the latter, verging on Pizzagate territory.