I love how it's called a "random attack" when you can see a couple fishing rods out in that video.
Bulls have two settings - on and off. I've had a lot of days when we have problems getting them to approach us in the water; most of the close encounters I've had are when there are a lot of them and the numbers advantage makes them bolder. Last time I was out of Jupiter Inlet we started the drift getting mobbed by small Caribbean reef sharks and it was actually something of a relief when eight bulls showed up to chase the little punks off.
If the victim was hit "as soon as he jumped in the water," I wonder if the shark just hit whatever made the big splash; sounds like it was a hit-and-run with no follow-up bites.