It's programmable and the values are stored in the instrument cluster. VW sets different maintenance reminders by region.
In the US, the maintenance reminder is set at 10,000 miles on TDIs. Some dealers reset them to 5,000 miles to extract more cash for oil changes.
You can change it with a VCDS. It's under 17-Instruments, then you click on adaptation, and it's one of the channels up in the 40's. There's another channel you can adjust to set the days between services as well. Whichever one gets hit first will trigger a maintenance reminder.