I had the opposite experience while snowboarding. I crashed heels over head going 20+ mph while wearing my Watch Ultra with my iPhone in my pocket. Neither crash nor fall detection was triggered. I was kind of disappointed since I’ve “successfully” triggered crash detection when I was hit by a car while riding my bike, and triggered fall detection when I jumped down from the 2nd rung of a ladder.
I’d rather my phone call for help and me be ok enough to cancel it, than need help and not be able to call for it.
Did you send details to Apple about your unreported crash so that they can improve their algorithm?