I believe the lines in question are the British "Laystrayte" brand control lines, which have been around for many years. Someone with more mathematical prowess than I can probably explain why they are less drag.

Les

Yes, yes, yes.

I suspect that the diameter of the line is not constant and the stranded wire is smaller in diameter as a function of the twist in the three wires that make up the total. Twisted sufficiently tight to measure the desired diameter when the required micrometer is used, but loose enough to yield the desired reduction in cross section.