The way Google Drive works, the files should be synced on a constant basis from your phone or computer to Google Drive in the cloud (assuming, of course, that these files are saved to Google Drive, or in the case of a computer, the folder that the files are in was designated to be synced to Google Drive). So I don't think those files would necessarily be part of the Google Backup process, since they should already be backed up/synced anyway.
Restore from backup | Android Central
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The thing about Google Backup is that it's used primarily to restore to a brand new phone (so you'd have to factory reset the phone and then go through the setup wizard to make use of the Restore function).
