I must be missing where it says that in the pattern. I've read it 3 times and can't see it. What part are you at exactly? Is it part of the chart pattern or the heel?
I'm going to guess that it's the pattern itself, in which case, I believe, you are reading the chart backwards. You work a chart from right to left (not left to right like when you are reading a sentence). So you would be doing a K2, slip one as if to purl (the yarn would be IN BACK), then bring the yarn forward and P3.
Maybe, I'm missing something, but that's how I'd do it. Yarn in the back.