I need to specify category to make the creation of advanced components compatible with "create_component_instance" function. Yes, "advanced" components are always of category "advanced".
Annotation components itself are not "problems" (although problems are attached to the annotation component).
So to create an advanced component we need its advanced_component (value different for each advanced component sended to xblock view as "category": "annotatable"), name of component type ("Annotation") and the category in which the advanced components exists (which is always "advanced").