The only "double stitch" I've ever heard of applies to crochet, not knitting. I have some of the "exotic" yarn, but there is no pattern on the inside of outside of the labels.
I personally would ditch the directions and find a pattern that used 60 sts and work the heel flap and gusset according to that. I've made socks with the exotic with standard knitting patterns and they've come out perfectly, so there's nothing specific to the given directions which are going to make them look any better. Unfortunately, the patterns I've used aren't for exactly 60 sts. There are formulas for figuring out the flap and gusset for any given number of sts but I've never needed them, so I don't know what they are.