I believe that you might be grossly underestimating my expertise. I know exactly what I am talking about. I do believe that you are the one here looking for help, and I am giving you the correct answers.
If you are so familiar with the program, you would be aware of the fact that the backup created in itunes does not store music files. they are stored in the itunes media folder
The reason that it is possible for the phone to get the music back after doing an update and restore is because the information is a. not erased from the device during the update, b. restored from the music files in the itunes media folder, or c. stored in iTunes in the Cloud, all of which are not in a backup
I am 100% certain this file does not exist in your backup