It's not really that dangerous, but you can easily roll over, if you lean to either side, especially when you lie deep in the water with 3 guys in one canoe.
They might have had somewhat a calm and it was on a sea, but what still matters is, the shock of falling in and the range to the shore (plus the direction at night, when you are drunk). Turn it back and climb in, is not a thing that works too well in normal conditions.
Sad thing, pretty shocking; We take so much for granted...

