The thing about having two sets of eyes is that the creature can see into multiple directions at the same time, so it notices them both and growls another growl, sending a stream of water to stop their journey. If they try more it will attack. If they turn around and leave it will not.

It's unclear if it knows they're the same people or if it thinks they're a shark and a orca, but it doesn't seem to want anything in its territory.