Do you mean the blue part? That's called the Scotch Stitch. It's larger than the Mosaic Stitch and it's for filling in large areas of background with something a little more decorative than tent stitch. Each block of the mosaic stitch has 3 diagonal lines. The scotch stitch usually has 5.
In the blog, the yellow background is a variation of it. The dark blue background for the Wart is the Byzantine Stitch.
Here' a picture of how to do a scotch stitch.
http://www.freepatterns.com/content/con ... ent_id=139
If you look in almost any needlepoint book, it should have several different stitches and instructions on how to make them.