Admittedly I have only basic P of F knowledge and a bit of ‘A’ level physics, but surely, if the rotor aerofoil is stalled then it is producing next to no lift. Therefore it is not throwing any airflow downwards to be re-circulated, if there is no recirculation you are not in vortex ring!
My image of the vortex ring state consists of the rotor disc producing lots of downwards moving air, now introduce a rate of descent (or upward moving air) and the downwards moving air can’t dissipate, instead it moves outwards and upwards where it finds a nice low pressure area immediately above the rotor disc, gets sucked in and round it goes again, and again, etc. Now we have the rotor disc ‘flying’ quite happily in its own ring doughnut of air – unfortunately, the doughnut of air will go wherever the rotor disc goes i.e. downwards!!
Downward airflow through the disc will surely reduce the angle of attack on the blades. Sorry, I can't see how you can disagree with Nick's explanation.
TeeS