I apologise I misunderstood your comment. You’re not wrong about the hazard. It’s a possibility. The risk is very low though. The warning is more akin to the warning that an accidental electric shock from a domestic appliance can kill. In the vast majority of cases it’s not fatal. But A very small amount of current accross the heart can induce fatal arythmia ( that’s why RCDs were introduced ).
The cold dip into a harbour I mentioned was used for many years without issue, on a wide range of people. They had generally passed a medical, which later had an ECG.
Cold shock is real, it hurts. The chances of inducing cardiac arythmia, fatal vascular complications , involuntary aspiration etc. are very low in a healthy individual.
Leg cramp in swimmers can kill too, but it rarely does.
My own first experience of sudden cold water immersion was not as an acclimatised swimmer but as a 16 year old in the middle of a tidal lake.
Unpleasant, Intercostal muscles spasm too it’s hard to breath etc. but if you’re a confident swimmer you will generally make it out alive