That's actually a slipped square knot. But the way you tie it is sort of reminiscent of a clove hitch. As he says on the site, you wind up with the same knot

That's actually a slipped square knot. But the way you tie it is sort of reminiscent of a clove hitch. As he says on the site, you wind up with the same knot (slipped square) that you'd get by the usual method of tying.