This is done by reversing a couple stitches over the top or just next to those machine stitches at the beginning or end of a line of machine sewing.

How to Back / Reverse Stitch:

Position the needle about 1/2" from the top edge of the fabric. Stitch in reverse almost to the raw edge. Change back to forward and stitch to the end of the fabric. Reverse and back / reverse stitch about 1/2".