Although described by Henshall as "unclassified chamber, round cairn" it looks just like an example of a Clyde cairn.
(The main difference between Clyde cairns and Hebridean Passage Graves - or, indeed, any other form of Scottish chambered cairn - is that Clyde cairns have no passage. The chambers start at the edge of the cairn.)
North Uist may seem a long way from Clyde cairn territory but nearby Clettraval is widely accepted as being a Clyde cairn. It has the more usual long cairn but Clyde round cairns do exist.
The edge of the cairn at Craonaval is not easy to see because of the vegetation but the two-compartment rectangular chamber is clearly visible.