Bet you are exactly right, typical, and a good way for it to fail, won't hurt anything except freeze the driver out.
Cheyenne WY area has always been bad luck for me, especially the climb from Laramie towards Cheyenne. Car-killer grade that will find and reveal any mechanical weak point, much like the Grapevine in southern CA. Trivia fact, it's the highest point on I-80 in the country.
Good chance that hill killed your tstat (or more accurately gave your end-of-life tstat its final push). Engine was loafing along on flat ground for hours up to Laramie, probably with a tailwind behind you to boot, and in cold weather, so tstat was most of the way closed with minimal heat coming from the motor. Then you hit the hill, put the pedal down, and the engine started working hard and kicking out heat, thermostat had to quickly open, and that just happened to also be the last big cycle of the spring that tstat had left in it. When the spring got compressed it snapped the crossbar off and broke the stat open. Came down the other side into Cheyenne coasting, and the engine temp dropped like a rock and stayed there, right?