When using a "rubber duck" I think you just force yourself to turn loose thoughts into coherent ideas by having to express them clearly. This can reveal some problems that were not apparent before the idea was expressed. It's a "rubber duck" because it's really just a monologue and an inanimate object could do the job of the listener.

What's described above seems more like Socratic questioning, where a person asks questions that reveal facets of an idea that the person being asked may not have considered, thereby prompting the asked to rethink their assumptions and draw new conclusions.