Look later on in the pattern, the CO sts are probably there. It seems like this part is tell you how to set up the rib st pattern, and it's not unusual to have patterns put this before the CO instructions. It may actually be that you cast on and start working in stockinette and this ribbing will not be the actual first rows of the pattern, but starts later on. Row 1 sets up the rib, row 2 is a common way to write subsequent rows for ribbing. If you knit what look like knit sts and purl the purls, you'll be knitting a rib.
sue- knitting heretic