Rokurou had definitely hightailed it back to thicker cover in the reeds, but since he's preoccupied with the giant oyster in his hands, he doesn't notice Naomi shifting. He looks up through the reeds to check, but he only sees the blots going insane. He can only assume that Naomi managed to get back in the water unseen somehow, so he ducks back under before he's noticed.

He could wait where he is, but he opts to continue swimming the rest of the way back to the entrance. If Naomi's in the water, she might be able to catch a flash of his tail as he quickly swims along the far shore.