I know you said "apparently", but how can you know this for a fact?
How can anyone's pain tolerance be objectively measured? I've always wondered about this...
The physiological signs of pain occur mostly as a consequence of the way we consciously experience and process pain. (This is why "general anesthetic" works: central processing of pain is required before sensory input is actually registered as painful, and so, without the brain there to decide that a thing is painful, the physiological consequences don't happen. Pain that would give you a heart attack if you were awake doesn't cause the slightest physiological problem when you're unconscious from general anesthesia.)
If you are receiving a lot of "painful-stimulus describing" sensory input, and you're consciously experiencing those stimuli as painful qualia—but your body shows relatively little physiological response—then you have a high tolerance for pain.
This can be measured by using a standardized painful stimulus (e.g. a sub-cutaneous injection of a standardized dose of some insect's venom) together with an fMRI (or just self-reporting) to measure the intensity of the painful qualia, and various physiological monitors (EKG, etc.) to measure physiological response to the pain.
I believe this has been done before specifically in the case of certain sects of monks who like to demonstrate the depth of their meditative ability by tolerating large amounts of pain. They did the experiment to try to figure out whether the monks are tolerating an experienced pain, or merely are somehow not experiencing the painful stimulus as pain-qualia.
I've watched first hand as the anesthetist has said "whatch the monitor as the surgeon does this bit" and seen the response.
(There might still be a local release of pro-inflammatory cell-danger-response purines from the wound site that do things when they hit various organs/tissues on their way through the circulation, but I believe we don’t tend to call those “pain signals”, for the same reason we don’t call them that in plants or fungi.)
True story, I had a major illness in my late 20s. And apparently I have a high tolerance for pain, so the nurses and doctors repeatedly underestimated how much pain I was in. I can be in incredible pain and still hold it together and answer questions in a calm and rational manner. This made one doctor suspicious that I was faking the whole thing. So then I tried to adjust my behavior. I started deliberately giving more outward signs of the pain I was in. And then the another doctor accused me of exaggerating or being a hypochondriac.
I was not able to find a level of external performance that kept all of my doctors happy. If I was too restrained, then they had trouble believing I was really feeling the pain that I described with my words. But if I tried to act the pain I felt, then I was accused of being a hypochondriac.
I should add that most of my doctors were great. In my whole life, I've only had 2 negative experiences with a doctor, the two that I just mentioned.