I recently didn't do that many miles at all but for some reason it appears that a previous renter did and they didn't track the mileage appropriately.
Got a receipt for a weekend rental showing I did 7600kms over three days.
I argued at the counter, afraid it may flag me (don't give him the good / low mileage cars anymore
) but they wouldn't change it just repeated that I had unlimited mileage anyway.