I don't know if it plays out any differently, if you already have the githyanki egg in your inventory but otherwise, you can tell Esther that you won't get involved and the matter is settled. The quest is not added to your journal and while you can chat with Esther about the experiment, it counts as a decision made and you can simply walk away. The owlbear egg is an option for characters who are a bit greedy or like to lead a cruel experiment astray, but it is not necessary to get out of the situation peacefully. I would even argue that giving her the owlbear egg is not part of a paragon playthrough at all, as it is a con.
Still, I agree that it should not be randomly fed to the cub, a situation during which you don't have control over what is handed out, unlike the long rest menu in which you have control over what you eat.
