This is one seemingly tiny, new feature of the device. He might not have bought the device for this feature, or even have known that it was there. Or rather, the people reading might have not bought the device for this feature, or even have known that it was there. I think this is what makes the story popular enough to be going around.
FWIW, unless you are over 60 it's not enabled by default. Presumably this is to minimize false alarms, but if you want this feature enabled, you should make certain it's enabled.
Additionally, some of us who have this watch and this feature enabled want to share stories that verify the feature works for some people ergo could work if something happens to us (and this also helps us to rationalize our purchase!)