As I mentioned during the KNX interview, it is really difficult to speculate on this incident from across the Channel and with the often contradictory reports that were coming out on the boards and in the media.
When I heard the attack occurred over a shallow (20-30 ft) sandy bottom, I was a bit surprised. However, we've had observed GWS attacks on sea lions over sandy bottoms here off Catalina (primarily near the sea lion hauling area on the East End). Generally they've been much deeper though. The only encounter I've had underwater was the one that swam leisurely by me and the artist Wyland as we were filming giant sea bass near the East End Quarry. That was over a sandy bottom, but in deeper water (70-130 ft).
The descriptions I heard of the attack and the wounds on both legs suggested to me that it was a typical GWS attack... coming up from below and behind the victim. This is why the shallowness of the water surprised me, although these sharks are capable of rapid acceleration. The fact that both legs were involved with the result being very serious wounds almost causing the lower legs to be severed suggested a shark in the 12-16 ft range to have a maw large enough to effect this injury. Of course it could have been even larger as suggested by a much better expert than I am, Dr. Richard Rosenblatt of Scripps. I have been underwater with GWS up to 18 feet... they looked like they could swallow me whole (and that's quite a feat!).
I would assume that the water along that stretch of coast is fairly turbid due to its exposure and the shallow, sandy bottom. Diminished visibility due to resuspended sediments would make it much easier for the GWS to mistake the swimmer for something more palatable.
As for anything provoking the attack, hunger is the most likely explanation. The fact that the GWS apparently just bit once and may have backed off, suggests it may have been a test bite to see if the victim was anything good to eat. The GWS is able to swallow smaller prey like fish whole, but the attacks in sea lions I've seen or heard of second hand suggest they hit the sea lion, possibly taking a big chunk out of the abdomen (or wherever they hit it), then back off to wait for the animal to bleed to death. We have seen sea lions dead, or still alive in the shallows or on the beach with such wounds.
When I first came to Catalina in 1969 I was quite fearful of GWS (all previous diving was in freshwater). I gradually realized they weren't the problem most media made them out to be. However, I stopped diving for about three years after "Jaws" came out. The fact that after the film I was introduced to a guy who had a HUGE scar on his upper torso from an attack off Pt. Conception certainly accentuated the fear. I didn't return to diving until "Jaws II" came out.