One does not need PITCH input to trigger the STALLWARN, only "G", as you say.
If so, and you say it is, we would be looking for sufficient turbulence to trigger G that triggers the STALLWARN. This can happen in a/p, obviously, and the STALLWARN will remain silent. So I seek the data that conclusively shows us the PITOTS were clogged, and in failure. Powdery ICE is thus far unknown to me. Perhaps it is hitherto not well understood by others?
I do submit that STALLWARN can trigger without my touching the controls. No "extreme maneuvers" needed. The STALLWARN can be a TURBWARN as well? Even a WINDSHEARWARN ?