Unfortunately no, I have not seen any explanation from Cruzz and it rather hard to guess.
Given thou that the number increases with lower scatter values it seem that takes that into account also...
Maybe average damage divided by average scatter area?
Imo would have to find the ratio of scatter area and AOE if one wanted to express accuracy for indirect fire weapons, so maybe that is waht Cruzz has done.
This is why i find it pretty bad as a metric to reference, when we don't even know exactly how it is calculated.
IMO, it brings more confusion to the discussion than rather listing scatter, AoE and RoF in separate ways.