I would bet that it's a separate piece that was formed and dried that way, then attached to the top. Just my guess! (That's how I would do it)
Ive done that cake and have the instructions.
You roll a long piece of fondant and then gather it. Dry it in a round container with some foam to support it. Attach it to the cake with some soft fondant and cover the seam with the ribbon.
I added some tylose to my strip to get it to dry faster.