I think what they were talking about was the methodology on sizing the cfm for a particular carb. 4bbl carbs are measured at 1.5 inches of Hg, and 3.0 for 2 bbl carbs. The quick and dirty is that a 2bbl carb rated at 500 cfm is 40% smaller then a 4bbl rated at 500 cfm.
So to convert a two-barrel rating into a four-barrel rating, divide the two-barrel rating by 1.414.
To convert the four-barrel rating to a two-barrel rating, multiply the four-barrel rating by 1.414.
For example, a 350 cfm Holley 2bbl flows 247.52. So to get the same flow as a four bbl 500 cfm, you would need two 350 carbs, or a 700 cfm two bbl, lol.
