Just to clear something up...
It is my understanding that any airliner is certified, at any speed, to take a single, sustained, application of full rudder, and then have that application released. Not good practice of course, but to achieve this rudder limiters are required.
However, a full rudder application made and then held will build up a sideslip angle. What an airliner is not required to withstand is, having established this sideslip angle, for full rudder now to be applied in the opposite direction. This is sufficient to exceed the design strength of the fin / rudder = may snap off.
I further understand this is basically what happened on this occasion. The question is who or what applied the rudder inputS - the pilots (seems pretty unbelievable for perceived "light turbulence"), some "automatic" system (yaw dampers), or the flight control system itself (hydraulic actuators).
NoD