I agree. Looks like a half log cabin block. Don't know why they call it a half, it's really a quarter of a block.
If you assume that they used 2.5" strips, then you would start with a HST that finishes at 4" (cut squares at 5", draw diagonal line, sew on either side, cut then trim to 4.5"). then add 2 rounds of strips. Strips added to the dark side of the HST.
Nice pattern!