Xperia S (LT26i) stolen. Can thief access internal storage?
The device storage is in fact the internal storage, just mounted differently, so if you erase the device storage, you will also erase the internal storage. If the bootloader of the phone is already unlocked, he could flash a custom recovery like twrp and access the files from there (over adb for example). But if the bootloader is locked, in order to unlock it, you need to erase all user data (internal storage), so the thief would not be able to access any data.