Well, on a 5mm wire rope, without knowing how many strands, or how many wires in the strands, Bank of Dad is correct in saying it's not the wire rope that's a concern but what it attaches to. The wires breaking strain will be roughly 1800 kgs.
That's a lot of beer that Holden Man is going to have to consume to before attaining his myth buster moment!
Kids jumping eh......yep that's what it would have been for sure...pretty sure when I was searching for a van read a few Rapids with bowed bed ends. They put it down to kids jumping or something.