Things all seem to point in the same direction (well, to me they do
The table was set for lunch. the engine was running in the background charging the batteries. It was stinking hot. There was no wind, zilch, nix, nada. The boys were on deck getting toasted. The sails were gently flogging. The fenders were not taken in when they left wherever they left from but were pulled up and laid on the deck, not uncommon especially on a cat with lots of deck space.
The boys were TOTALLY becalmed and decided to go for a swim before lunch. One sensibly said "No, I'll wait on deck until you guys are done". The others said "Ah, come on, just a quick dip. After all, the boat's standing still isn't it". So he let the sails completely free, put his clothes on the deck, took off his glasses and put them on top and dived in. His dive may have even pushed the boat the first ten feet.
But then a little zephyr came along and moved the boat another 20 yards. All three swam for the boat and as they reached out to touch it, it went another 20 yards. There are only so many 20-yard stretches that a 60-year-old can swim before the boat starts to open the gap. Finally they are too knackered to go any further and the inevitable horrible truth becomes real. They're never going to get back on board again.
Some time later the wind came up, the headsail was completely free and flogged itself to pieces because the boat went head to wind. The mainsail doesn't have the same motion and wouldn't suffer the same damage. A headsail flogging for hours will do exactly the damage that was evident. And the motion of the boat in the rough weather also tipped the fenders off the deck.
In reality, when I was a lot younger and a lot less cunning, we all went for a swim without sails up and it was suprising how quickly just the windage on the boat moved it away from us. I am a big fellow and a strong swimmer and with a huge effort was able to catch up with the boat but today I never go over the side for a swim unless there is 100 feet of rope trailing.
No, there is no sinister element here, this is a simple but fateful error made by three guys, easy done.