I've taken a look and the problem you have is caused by the geometry type of the collision Sphere. The spehere you use is a primitive. Now, as far as I understand, primitives a actually points. So the only way Houdini can interpret this type of geometry is as a packed rbd object.
I've added some new geometry to your scene, and I have set the sphere and cube to Polygon as primitive type. Now it works as static objects. I have attached the scene. You will see, when you dive inside the new sphere and box node, that the primitive type is set to polygon, and that works as Static Objects.
Hope this helps!
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