It's an on camera flash outputting at a higher color temperature (bluer) than the ambient lighting behind the two main subjects. The flash appears to be a typical 5500-6000K or so full spectrum light. The background appears to be more limited spectrum lighting centered on about 3700-3000K such as is typical with older tubular fluorescent lighting.
The camera appears to have been set to match the color temperature of the flash. This makes the ambient light look yellow/orange. If the color was adjusted to match the light source in the background, the two main subjects would appear very blue.
You can see from the shadows under the chins and the highlight reflections off the flat skin facing the camera, that there is a bright point-ish light a little above and left of the camera. This by itself should immediately suggest a pop-up flash on a point and shoot camera.
The "snapshot" nature of the picture suggests a photographer likely to use a point and shoot camera. These kinds of cameras often have integrated flashes.
The color analysis by Michael Clark also strongly points to a flash.