I'll just go ahead and dump a theory on how "dim mak" came around. It's total bullshit, but it's probably closer to the truth than reliably being able to kill with a touch.

Martial artists and religious students living in a temple for decades spend time learning new and creative ways to hurt eachother beyond the obvious "big stick to the side of the head" trick. One day, one of them goes out for a walk. Drunk Dumbasses A and B are walking down the road, and Drunk Dumbass A decides that this martial artist doesn't look so tough and wants to prove how much of a badass he is. Drunk Dumbass A throws a punch at the martial artist and gets whacked in the side of the neck beneath the jaw. It doesn't look like the martial artist put much force into it, but he definitely did. Drunk Dumbass A stumbles around, falls over, and loses consciousness because his blood pressure dropped. Drunk Dumbass B runs screaming back to the bar and spreads a tale about how there're men who can kill with a single touch, and the story spreads throughout the bar quickly. Meanwhile, Drunk Dumbass A is just now getting back up. The two will meet up again later that day or maybe the next day and Drunk Dumbass B will realize he's wrong, but the story's already out and spreading like wildfire.

Alternately, Drunk Dumbass A has an undiagnosed and otherwise undetectable heart condition, and a strike to the neck causes a blood pressure drop that ends up killing him. In that case, the story is true, but only in that specific situation. Drunk Dumbass A would've died of it a few months to years later anyway, but the story's already out and nobody's going to bother with investigating it because that would take effort and people like spectacular tales.