There is a discrepancy in the mileage only because they use a key reader for the mileage. He probably had both keys and they read the key which had been used last at 24K miles. I'm sure the repair mileage is somewhere in between the two mileages. I wouldn't be too concerned.
It's a trick some people use to extend their warranty a bit longer....bring along the 2nd key and hope they read the mileage from that key.