Kinkoi spoilers, I suppose. I take it this is the explanation for how Ria's route in the fandisc works, unless they decide to actually go into more detail on this. I don't think I'm making any stretch to make the connection between a clam and the Orohora box, since they both open the same way and contain an item inside, and the Orohora box they get in this timeline is the one that Ouro threw in the lake at the end of Ria's route in the main game.