I don't know the circumstances of the photo. I suppose it could be part of a project photographing supermarkets. But my guess is that it's plucked from daily life. Hansen was probably buying something at the market, saw this scene develop, and captured it perfectly.
To me this image is a reminder that potential photographs surround us constantly. Photography isn't something that can be stopped and started at different times throughout the day or the week like some assignment. Photography, at least the way I've come to practice it, is with me 100% of the time. For the past ten years I have never been without a camera. I'm guessing Hansen is the same.
There are admittedly some problems with this method. There are probably certain elements of life that are better approached without a camera, at least initially. When photography bleeds into every corner of one's world, nothing is sacred. Something is given up. I realize that. But that's just the way it has to be. I am no more able to turn on and off my photography than I am my breathing.