Except the theory they give makes no sense
Ovenden speculated that the two species began mating in response to environmental change, as the hybrid blacktips are able to travel further south to cooler waters than the Australian blacktipsThat would have always been the case, the hybrid advantage of greater range would have been there before global warming. If anything warming oceans would have been an advantage to unhybridized Australian blacktips which could then go further south anyway.
It might make sense if the oceans were cooling. That would put environmental pressure on all blacktips and restrict their range. Hybrid blacktips could then fill the environmental niche of the waters which unhybridized Australian blacktips had had to abandon.
It was a touch of sarcasm. Sharks have been there, done that before there even were T-shirts. ;)