Local residents firmly believe in the existence of the shouting even when they can't hear it, proving that this situation has occurred more than once. So even when they hear nothing, they choose to firmly prevent it, rather than dismiss it as a child's prank or fantasy.
If this inference is correct, then distinguishing between a true "Hidden Friend" and a player role is quite easy.
Another key point to pay attention to is the issue of who gets to play the role the game designates. They can't choose the wrong person, nor can they be unable to find a person, which means they can't target local people or non-dungeon players, and as "Hidden Friend" only needs one friend each day, it indicates that one player must disappear daily, no more, no less, no matter how the role shifts around, only one player can disappear each day.
Today two people disappeared from the instance.
