That is exactly correct. It is a teaching exercise, not really a muscle-building one. It can be used to build muscles but the romanian deadlift can do that same job better.
I never used the duck walk. I remember one of my friend who ran track and was a fellow training geek telling me that it was actually a potentially dangerous exercise to use. I don't remember the exact reason, that was about 18 years ago, so I never thought of it again.