Sounds to me like they replaced the pads but not the wear indicator. If you reset it now, it will just show four dashes (----) on the display and throw up an error every time you get in the car.. Very annoying! Did they charge you for a new wear indicator? this should be replaced when they do the pads, especially at a main dealer!
The way it works is that it is attached to the pad and sits against the disk and wears down as the pad wears down, giving a reading of estimated mileage left until the pads are fully worn..