The Khajiit in the picture is also holding a bow, which means that the positioning of the legs could just be a result of the stance for holding weapons. This picture really doesn't tell me what Khajiit legs are like either way, which might be intentional, either because they are indeed digitgrade and Bethesda wants to keep this secret so it can be a surprise later, or because they are not digitigrade and since Bethesda knows some people want digitigrade legs, they want to conceal this fact as long as possible, of course, a third possibility is that no particular effort was made to conceal the structure of the legs or feet and that just happened to be the way the picture was taken, since Bethesda wanted to put emphasis on the upper body rather than the lower one.
They are either plantigrade - walking of full foot (Human) or digitigrade - walking on tiptoes (Cats, for instance). The backwards knees or whatever you call them are actually heels.
You are right that the whole "backwards knee" thing is a misconception, although I do seem to recall that Morrowind's Khajiit and Argonians had their actual knees somewhat bent too, but that was a result of the animations for them and I wouldn't say it's an inevitable result of digitigrade feet.