On each half, there is a soft piece of fabric that covers all the other seams and give the case a nice soft finish. The seam is visible on the outer part of the case, now that we pushed the teeth of the zipper down. It is held on by 2 threads

The first thread goes through the leather, makes a loop, and then goes back through the same hole. It then moves a few mm and repeats.

The second thread just goes through all the loops

Sew pattern schematic not to scale . It's just to get an idea of how the fabric is held on. The threads are pulled tight. They were most likely machine sewn