Device storage size shows a lot more then app storage

My child's install of MCPE 1.7.0.13 on his Kindle Fire HD8 within the Freetime profile. The system shows 17GB of internal storage being used. The app storage settings only show around 1.3GB worth of data being stored. 

I've tried moving the app to the internal storage or SD storage via the device settings, but it changes nothing.  There's no option to move the storage in the application itself.