I have seen the video before and knew very well that the chart is extracted from this video published by Brompton and there is something erroneous on the chart, either the drawing or the statement that the chart show the gearing of the 4s and 12s with the same chainring size.
The 4 sprockets are the same on the 4s and on the 12s and the BWR hub has a 1:1 ratio on its second gear, so with the same chainring size, the gear inches must be the same for the 4s and 12s on its IGH second gear.