The first point is that the number of players in the dungeon has become 20.
The second point is the notification that he has already cleared the dungeon.
When one person clears the dungeon, it signifies the end of the dungeon, and the remaining players all fail to clear it, but they can leave nonetheless.
Upon seeing the message of clearance, Xu Huo realized that having one person clear the dungeon doesn't mean only one person can clear it, but rather that as long as one person clears it, the dungeon ends. Previous players probably hadn't realized this and mistakenly thought killing someone was the way to clear it.
Of course, every time the remaining player count in the dungeon updated, Xu Huo also assumed the missing players were dead, killed by fellow players or by the true Hidden Friend.
But the dungeon's intent is not to kill, so as long as someone sees the dungeon's hint, it doesn't even need to result in any deaths.
