No, not that (unless I'm misunderstanding you, which of course I might be). Here's what they do, according to the PDF that I linked to:

1. Illuminate with two IR sources, more or less on-axis and at known positions relative to the lens. 2. From the ratio of the resulting pixel intensities, estimate per-pixel distances. 3. Take each pixel from the image whose camera is focused nearest to that pixel's distance.