In short, the blade has a low but positive pitch angle with respect to it's plane of rotation, with the collective fully down (although I believe the Lynx can apply negative pitch - correct me if I'm wrong here).
In autorotation, the rate of descent means that there is quite a deal of airflow coming from below the rotor. Add to this the 'oncoming' airflow caused by the blade's rotational speed and you get the resultant relative airflow that the blade 'feels'.
Lift is produced, perpendicular to the relative airflow, and also drag, parallel to it.
Because a lot of the relative airflow is coming from below, the aerodynamic force produced by the blade can be thought of as being tilted quite a way forward (thinking of the advancing blade makes this easier to picture).
Resolving this force in both the plane and axis of blade rotation, you get lift (keeps the machine flying rather than falling) and, surprisingly, a component that acts to keep the blade turning like a windmill.
So you don't need negative pitch, it's the rate of descent that does the magic.