This is Australian javelin thrower Reg Spiers, best known for literally mailing himself in a big giant box from London to Australia in the 1960s:
Spiers was broke and needed to figure out a way home to his family, so he did what any person would have done: he posted himself.
That is because the eyewitnesses were told that it was impossible, and that they must have been mistaken.
That film was crap in every aspect anyway. Saw it in the 90s and even then it was cringe.
These might not be life jackets at all, but more like what we do with seat belts and airbags now.