Shark eggs are thought to give off a protective substance to protect them in the wild from predation. Your trigger may have been subject to that by biting into them.
That said, Triggers and sharks are not usually a good combination as the triggers can easily damage a shark's eyes or fins with their teeth.
As for the biting of the rock, Triggers actually use rock and corals to sharpen their teeth so biting it is "normal" for the specie.
Hope this helps