Understanding the Issue
What happens and why
Performing a factory reset will not delete all data (e.g., pictures, music, etc.) from the internal device memory unless you specifically choose to do so.
Help & How to
To perform a factory or master reset and delete all data on the internal memory, on the Factory data reset menu, scroll down and select the Erase all data check box is selected.
Note: Erase all data only when troubleshooting or when issues impact the device storage. Follow steps to back up data before a master reset for pictures, videos, and personal content.