This pattern seems to take advantage of the fact that you need to knit 2sts to bind off one. So you need to knit 1 extra stitch in order to work the bind off of one:
knit 5, cast 1 off, knit 2, cast 1 off, *knit 4, cast 1 off, knit 2, cast 1 off
{repeat from * to last stitch}, knit 1 (end with 22 stitches)
You’ll end with 4sts, a bind off, one stitch, a bind off (3sts, a bind off, 1 stitch, a bind off) x4, k1.
That adds up to 22sts.