K1B: K1 in front of st in row below, k st on needle
The way I read this, they're telling you to knit the stitch on the previous row, then knit the one in the current row before you pull the stitches off. Normally you'd pull both stitches (the stitches on both rows) off together which would result in no increase. But if you knit both stitches individually, you'd get ... two stitches where there used to be one.
That's what I see, and probably they should've called it something else (though I don't know what the real official name for it would be) to avoid this confusion.
Just my 2% of a buck.