Two classes of hot Jupiter a statistical artefact?

It is starting to look like the classification of hot Jupiters according to Safronov number isn't holding up too well: the division between the two categories may have been a statistical artefact.

arXiv: Homogeneous studies of transiting extrasolar planets. II. Physical properties

Is/was the Safronov number the discriminator between pL and pM class hot Jupiters? Or was that atmospheric properties?

pM/pL was a different system.