"It is impossible to die from hypothermia in cold water unless you are wearing flotation, because without flotation – you won’t live long enough to become hypothermic."
Or it's in shallow water. I once fell through ice over a frozen creek and was close to hypothermia before I found another camp group after I'd been inadverntently left behind by my parents during a winter camping trip (each of my parents thought I was with the other). I was soaked in about 10F temps, but I was able to warm up, but not dry out, next to a fire. I was 9 or 10 at the time.
His facts are a little off, but it is a good article. For example, he states, "When the water is cold (say under 50 degrees F) there are significant physiological reactions that occur, in order, almost always...You Can’t Breathe"
But he's painting with a too broad brush. In other words, some people experience those symptoms, others don't. For instance, my fellow swimmer Brenden Sullivan swam in Tahoe at 38º F (well below 50) and didn't experience the can't-breathe symptoms).
Few people in the open water swim club that experience the loss of breath: most people get in the water & start swimming without problems. I do experience the loss of breath when the water temperature drops below 52º F:. In fact, I have to do backstroke for the first 50 yards before my breath normalizes. But I'm the only one I know who suffers like that.
Also, body fat makes a big difference, but muscle, not as much. I've seen too many body builders shiver in the sauna after swimming in the Bay. Body fat makes a big difference; big-time open water swimmers are not svelte.
https://gcaptain.com/cold_water/