No one at B&N customer support will be able to help. They have no clue what they are doing.
Rignes, I don't think this is a B&N feature. I think this is an Android feature related to Goolge Play Apps. So if you search for 'Android App Data Backup' on Google you'll be able to find out more.
You can also test by installing some app from the Nook App Store. Save a bit of data, then doing backup and then uninstalling the app. If you can't get the data back on fresh install of app then it probably means the backup feature is limited to Google Play Apps. I know it's been a feature for Android in the past. So it's probably due to Google Play being added.