If there's a loot box with a 50% chance of a cat in it, no game developer in their right mind would bother determining if there actually is a cat or not until someone checks.
That depends on if the developer wants to allow RNG manipulation speedruns or not.
Actually, the opposite - a good dev would simulate two outcomes. Otherwise you may have a serious lag the moment someone opens up the box, because the system would need to simulate the cat’s behaviour for the past.