I had a similar thing just two weeks ago. Car came in for some warranty work which did not require them to drive the car and when I got it back it had 6 miles on it. My invoice looked like yours where in and out miles were the same.
If you will be purchasing ANY AT&T services online or in store could you mention that you were referred by me? My Employee Referral ID is eo4489. This would be a great help and it costs you nothing, thank you!