Safetypee;
the PF decided that this alert represented a real stall and commenced the erroneous action
IMHO you are reversing cause and effect.
Therefore there may not have been an immediate association between loss of an airspeed display and a drill relating to ‘ice crystals’ and aircraft handling.
Loss of airspeed display means that you have to manage flight without it. In cruise that means maintaining current attitude and power setting, not pulling to climb.