These are probably offsets to the texture. If they use a 1024x1024 resolution for the shadow map, and since tex coords are in the [0-1] range, an offset of exactly one pixel would be 1/1024 = 0.0009765. Now they’re probably using a filter that is not perfectly aligned on pixels (like circularly around the pixel’s center), which explains why you don’t get exactly this value. You’d have to draw it on a paper to see exactly what they’re using.
These numbers are “random” points in a Poisson distribution around the origin. Their exact positions are shown in some graphs and code in this presentation on slide 29 and slides 43-46.