The scientists claim their new data matched all of the tracking information from the disappeared shark: The body temperature they registered was the same and the size of the cannibal great white shark—which they estimated to be 16 foot long and weigh over 2 tons—could easily pull off the same speed and trajectory captured in the tracking device.
It makes sense: The only thing that could reasonably eat a shark is something that resembles a shark, only bigger. The bigger the shark, the bigger the bully. The studies show how smaller sharks immediately vacate the waters when they sense a giant one is nearby. Well, that and krakens and kaijus and secret weaponized alien megalodons.
As for why a larger shark would cannibalize a smaller shark, the study suggested theories about how it could have been attacked. Maybe it was a territorial dispute. Perhaps even a hunger induced attack. Finally it settled on a hypothesis that makes the most sense: Big sharks eat little sharks.