BIg surface.. big forces.
The roll was due to yawing a swept wing - not the rudder. Left rudder, by itself, would tend to create a roll to the right since the vert is above the aircraft Cp, or cg. The resulting roll to the left is due to yaw, or un-sweeping the right wing - increasing lift on that side, and increasing the sweep of the left wing - decreasing lift on that side. Hence the roll to the left. Works subsonically and transonically.