i have talked to a couple of pilots who have had jack stall happen in the mountains, both in very benign phases of flight (cruise and cruise descent respectively). they were not performing aggressive maneuvers or in any way abusing/throwing around the a/c. they both experienced stiffening of controls which went away after a few seconds, and were at sufficient altitude that it did not endanger the flight. their best guesses were that there were mountain wind currents that momentarily loaded the disc in some way that overpowered the servos.
i think to insinuate that all pilots that experience jack stall are in some way flying like cowboys (though surely SOME are) is going a little bit far. one of the aforementioned pilots had over 13000 hrs, with multiple thousands in a-stars, before he experienced it.