I think they're counting the sum of the two parts as a single row. That is, with something like this:
The XXX is a single row; you then bind off stitches in the middle, leaving you with two halves (YYY and ZZZ), but "one row" is YYY+ZZZ.
Basically, what the instructions are telling you to do is bind off both of the shoulder areas (YYY and ZZZ) going from the outside in. After you bind off the center stitches, and knit to the end, you're left with 20 stitches on each end. You turn around and bind off the one partial-row of stitches, and then you need to either cut off that yarn or start a new one for the other side (so you aren't carrying the yarn across the gap), go across the rest of the row like normal, turn when you reach the outside edge, and bind off the remaining stitches.
(It doesn't look like it'll be /much/ shape to the neck, since you're only binding off one row before
But I don't know the pattern, so.
And yes, ending with a WS row means that you'll just have finished a WS row when you stop.