The .dat files you are seeing in the same location as the local backups created by BackupBuddy are legitimate files used for the new “Restore Backup” feature (from within the WordPress dashboard) which is done directly within the site on the BackupBuddy -> Backups -> Restore Backup tab.
The .dat files enable additional restore features and are used to quickly get information about local and remote backup files when using the new “Restore Backup” feature.
If the .dat files are causing an issue, you can always disable them here:
wp-admin (dashboard) -> BackupBuddy -> Settings -> Advanced Settings/Troubleshooting -> Technical & Server Compatibility -> Disable .dat file creation
By checking that option then saving the settings.
But doing so, may keep restores from working as effectively when using that new “Restore Backup” feature from within the WordPress dashboard. So please keep that in mind.