This happened to me previously at IAH.
Had a BMW 528 that was checked out saying I had 9k miles, when it really had almost 28k.
When I returned it, the system wouldn't let him check it back in and required me to go up to the main desk. The lady at the Main Desk said, oh if you drive over 500 miles, we do a manual return to verify, but then she was like you drove it 19,000 miles in a week? I said obviously not (really had driven like 500-700). She was able to fix it, but I was amused at the difference.