Well, upon closer inspection, that upper rack looks like it would fit my KDS-17A, but... the existing top rack is in great condition, so I don't need it.
There is no wash arm or provision for one, so I don't think this top rack would fit the 21, or other KA dishwasher with upper spray arms.
Can't tell what is up with that supposed lower rack, although I agree, the high mounted side rails make me think "upper rack".