Blow the photo up and look at it closely. The squares are one piece, no seams, embroidered, not fussy cut. It does not appear that the squares have been appliquéd over the four corners of squares beneath them (meaning there is no bulk beneath them), but since the four edges of the squares have obvious embroidery on them, it's possible that they were indeed appliquéd. It is a standard tessellated octagon and square pattern with single pieces for both the squares and probably also the octagons. The logical way to recreate it is with set in seams.
If you want to go fast and easy, then snowball it, but that was not how this example was made as there are definitely no seams in the squares.