the attack of one predator on an other can have many different reasons.
checking out what that swimming thing really is, beeing mistaken by the look of such swimming thing, feeling intimitaded by that swimming thing, seeing it as a competitor for the prey they have a eye on at a moment and then there is the most common "reason", when a shark attacks a human in the waters of our country, which is that that human carries on a rope/wirehis/her prey hunted down by speargun, nicely bleeding in the water to attarct attention, so in those cases the ättack" is not even on the Human, it goes on the fishes lined up on the wire of that buso,fishes which are normal part of that shark's food variety.
Are you running for public office?