Painting with light is actually a term used for paint with flash of a large object when there is little or no ambient light.
A car or any other large object that needs more than just the ambient light is a good example of something that we might want to "paint with light"
Here are two images one with the existing light no flash added and one where we walked around the car and flash was used multiple times, the subject in the one we used to paint was playing in front of our camera and is a good example that we used a long shutter speed (aprox 30 seconds)
ISO was 50
There is no flash mounted at the camera, we simply walk around the object and fire the hand held flash unit multiple times, as in multiple brush strokes with paint, but in this case light !
Therefore the term paint with light.