Well, I’m coming to the conclusion that the writer of this design could have made it a lot simpler, and better. After knitting the foot and ankle section in the round the writer has us cast off. The foot sole is then knit as a flap attached at the toe as shown here.
The next steps are to knit a separate lace border and sew it to the cast off top, and to sew the sole piece in place. So there is quite a bit of seaming in this tiny object!
As I have knit it I have concluded that it would be possible to knit the sole first and then pick up stitches around the circumference for the foot. A nice little knitted frill could be grown on from the top of the ribbed section without the need for a seam.