I have seen something similar, using a sheet of sticky labels. She coloured a section of labels, stamped the image, then peeled them off and re-laid them onto a backing sheet. Could also maybe that the dividing grid is actually cut out on something like the Silhouette. and laid on top?(that actually just gave me an idea, lol).
Here are some similar cards on my blog, you could just round the corners with a corner punch.( now I have another idea, lol!)