I have been around for while and have done the rudder hard-over on the -400 in the sim.
Scary , no question.
But why speculate on yaw being added ?
Never seen anywhere close to 180 deg/sec roll in any wind shear sim. training.
And my company has the latest and the best sims.
For what its worth , I suspect somebody disconnected the autothrottle and mishandled a level-of in severe turbulence.
It can go pear-shaped from there easily and is a much simpler explanation.