Large Squid rise to shallower waters to hunt at night. It's more likely that a squid attacked the shark then. They are very aggressive.
The shark may have been using pilot whales as a way to detect deeper prey for it to feast upon - and that's when it found the giant squid that left it with scars.
Pure speculation. I doubt that this has ever been observed.
There is a theory that sharks have a particularly fondness for giant squid meat, with researchers claiming they are seen hanging out in an empty patch of ocean.
That may be true, but being cold-blooded sharks may have a problem digesting any food that they may catch in shallower waters. From an energy standpoint, why would a shark 'invest' that much to search for food that they can't really detect all that easily and where their intended prey can turn the tables on them?
... meant to say “deeper waters” with regard to the shark’s digestion.
Still wonder about the “empty patch of ocean.” Sharks could feed on squid coming up at night, but it would seem that the squid would be coming up to eat sharks, if the area is otherwise empty. That would make the noted sounds more common, it seems to me. Unless the sharks and squid are feeding mostly on pieces of the ones that do get into battles.