by Ken Task.
If the interface shows autobackup is off but it's still scheduled to run in the DB you might have to use anything you have (like phpmyadmin or other tool) and set backup_auto_active in mdl_config_plugins to '0' (zero)
Do leave your cron job running, however, as you will experience other issues if it's not run regularly ... like every minute. Check the task list for Automated backups and disable that task.
You can, as you have discovered, manually remove folders and files in moodledata/temp/backup/ with no ill affect on the system.
'spirit of sharing', Ken