Being an Aussie brought up on the east coast
I cannot recall
until much later in life meeting anyone who could not swim.Body and board surfed way offshore
before my teens swam at a competitive level but would think my chances if falling overboard
close to zero of swimming my way out.I must also admit I am starting to think more about things in the ocean munching on me the older I get.
The comment on most people equating swimming to a pool as opposed to the ocean would I think be relative to the country and area you are from but I think overall it would be the ocean.
As for the old timers my grandfather who was a master mariner born in the Shetland Islands could not swim a stroke and in fact had to be rescued by his crew somewhere in the pacific when he ended up in the drink.