It must have been too cold for him his heart gave way, (7)
Instead of reflecting too much on the dead man's life, the speaker or speakers here try to grapple with the immediate situation: his death and its cause. Sure, they're gossiping and ignoring the real issue, but they're also trying to force death to make sense. Which is a pretty difficult thing to do. So they go the CSI route and get all technical about cause of death.
Oh, no no no, it was too cold always […]I was much too far out all my life (9 and 11)
By repeating an earlier statement and taking on the others' comment about the coldness of the water, the dead man tries to get them to understand that death wasn't just a single moment for him. He always felt the deathly chill of isolation, as long as he was alive. This is an even scarier situation than the talking corpse of the beginning. Here he suggests that in a way he was always dead, or that life is only one long moment of dying. In the face of that idea, we would probably prefer to speculate about a heart attack, right along with the people of stanza 2.