might just be how they define it.
there are actually 3 conduction modes possible: continuous, discontinuous, and critical. there is also inductor ripple vs capacitor ripple, both of which cause the component to heat up.
frankly some of that stuff annoys me since some like to do their own derivation using their own terminology and it takes almost as much derivation to get to the conclusion that it is or is not a variation of the same thing.
not having looked at the documents, it actually sounds like the ratio is peak-peak to average putting critical at 2, continuous below and discontinuous above. likewise CRF would then be peak to average.