Why does the total mileage shown for a favorite appear incorrect?

The following was obtained from Garmin Support, Frequently Asked Questions.

The mileage shown on a favorite or saved location is the total distance to that location in a geographical straight line ("as the crow flies").

If you want to find out the total mileage for a route:

1. Touch Where To?
2. Touch Favorites or Saved
3. Select the location you'd like to navigate to
4. Touch Go!
5. Access the Trip Computer

For most devices, touch the data field that displays Arrival Time or Speed

If the Arrival Time or Speed field does not display the trip computer, touch the menu button and then touch Trip Computer

The Trip Computer will display the route's total mileage next to a checkered flag.