If you are taking the car and stopping at a specific restaurant, it's considered a separate stopover. It will count towards your limit of 5 stopovers per trip.
If you go to a restaurant near one of the stopovers, then it's NOT considered a separate stopover. For example, if one of your stopovers is Nami Island and you go to a restaurant inside or near Nami Island by walking (without taking the car to go to the restaurant), it's included in Nami Island.
Reasonable stops at rest area along the highway is NOT considered a separate stopover. You can often have lunch in these rest areas.