As another diver, I can confirm this. I can't really bear cold water dives. Heck, after an hour or so I can start shivering even in shallow 80F/27C water. There's a lot of variables involved. Age, weight, gear, time, depth, training, fitness level, etc. can all determine if your stay in the water will be somewhat pleasant -- or a miserable bone-rattling shake-a-thon.

So I really can't say that those unfortunate folk should've just struck out in unknown waters in the dark.