"The screen uses fiberoptic cables to spread light evenly across the screen when reading with the light on."
Light sources appear to be from the rows of LEDs around the frame, but distribution of light could not happen the way it is described in the quote above without the cables being noticeable in front of the e-ink screen. Maybe a mash-up of the two?
Let's call it built-in lighting, then.
We worked on Kindle Paperwhite for over two years to perfect the uniformity of the built-in light, flattening out a fiber optic cable into a sheet, and nanoimprinting to ensure perfectly even distribution of light. Our design uses nanoscale optical diffractive patterns to enable tight control over the direction of the light. Enjoy reading with exceptional lighting uniformity and evenly balanced whiteness across the entire display.
It appears that they actually do direct the light down from the light guide layer. It is most definitely not just LED's shinning in from the sides.