Seems little margin for error...
Given the article states:
... catastrophic structural failure at "just above approximately Mach 1.0".
... the system must be unlocked prior to reaching Mach 1.8.
It appears there's little margin for error there - I wonder what the actual safe unlock speed was supposed to be? Mach 1.7 ?
I also wonder if it was known that the actuators would be overridden by aerodynamic forces to cause such a movement at Mach 1.0
Unless there was a very specific procedure: "Thou shalt only unlock between X and Y speed", then it should not be classed as Pilot Error.