Having said that, slowing the rotor RPM a little during the descent would reduce ROD, no?
That depends on your RFM - if it says you can then it should specify a figure (on the Gazelle it was 330 Nr down from 380).
If it doesn't say you can do it then it is vital that you stay within your prescribed Nr limits. as you raise the lever, you move the 'driving' section outboard and increase rotor drag at the root (and possibly at the tip as well).
Overall you could see an increase in rotor drag which will need an increase in RoD to maintain the Nr.
Most people like to have as much Nr as they can for the EOL at the bottom and, even if you do droop the Nr for range you must recover it to normal for the EOL or run the risk of it being very exciting as there is not enough kinetic energy in the rotor to adequately cushion the touchdown.
As postulated earlier, it may well be what this chap did at Lumberton.