Odometer Mileage Spike

1996 Grand Voyager (nick named Hogwart) went to a local mechanic to have a body control module replaced (when the head lights were on there was a clicking from the under dash fusebox that sounded like the steady turning of the wheel of misfortune). It went in with the digital odometer reading 150,597. When it came out, the odometer was over 162,000 miles (approx 12000 increase - exact change is unknown). The mechanic is honorable and can’t explain it. Any ideas? Oh, by the way, Hogwart also has a way of making its windshield wipers randomly turn on for one or two swipes without drive control. Maybe this is a clue?