That's a good question, maybe I'll mention it with the link, since it's a beginner pattern. That just means, with the "wrong side," or what would be the back of the work, facing you. In stockinette stitch, the purl side is facing you. In this case, since it's ribbing, both sides look the same! And, furthermore, binding off on the "right side" would only mean knitting one more row, and on that pattern, it wouldn't make a noticeable difference. So don't worry about it. Either way you'll be knitting any knit stitch you come to, and binding it off, and purling any purl stitch you come to, and binding it off. Just basic knit and purl bind-off's.