I suspect that the light output from an LED source is not truly continuous. You are in North Carolina where the mains power operates at 60 Hz - so I would expect that the output from LEDs would fluctuate at 120 cycles per second. This happens because LEDs are DC devices that are powered from a full-wave rectifier that produces an output ripple at 120Hz. There is usually a smoothing capacitor in the LED ddriver to minimize this ripple, but it doesn't go away entirely. As a result, the actual light output from the LEDs fliclkers, but normally this is slight enough, and occurs quickly enough, that it is not perceptable to the human eye.
But a camera is different. I don't understand how the shutter in a cell phone camera works, but in the old days of focal-plane shutters on film-type SLR cameras, the shutter was actually a slit aperture that moved across the film plane during the exposure, with the width of that aperture determining the exposure that the film received. So if the camera was used to make a photograph in a situation where the light was actually flickering, it was possible for the actual exposure on the film to show variations like this. You may recall that one of the quirks of those cameras is that images of TV screens often displayed diagonal stripes that came about if the chosen exposure speed happened to synchronize with the scan rate of the TV cathode ray tube.