I believe it is relative to a TRS 3.5mm SE and it is more about avoiding the potential crosstalk issues from TRS to RCA cables/ adapters than reducing them: inevitably, TRS-RCA cables have a common ground section, which could be very short (just the TRS connector itself) or quite long (from the TRS connector to the “Y” branch out). If the impedance of this common ground section is non negligible, it will affect crosstalk performances. Interestingly, some headphone cables used (use?) this old trick as a simple “cross-feed” effect—an unusually high impedance single cable can be an indicator…