Sharktopus is a badly acted, terrible special effects laden Syfy Channel movie. However, it's a parody of Syfy Channel's own movies while being exactly like them.
The second Sharktopus in the sequel only starts killing people after being taken out of its tank and forced to be a bio-weapon to fight the Pteracuda. The thing was forcibly taken out of the only environment it'd ever known and forced to battle with another monster. By the time it's controller is destroyed, it's probably just a scared animal lashing out at it's unfamiliar surroundings. Once it's home, it only kills it's keeper's owner after he EXPLICITLY says he locked said keeper in a closet. Given it's part OCTOPUS it likely understood what he was saying.