If she looked closely enough, she could even identify those people, which included the Black Guards and the various sects' disciples. There were a few people she couldn't identify though. They were likely to be people who had entered the Mystic Forest on their own and ended up swallowed by the ground.
It had never crossed Shangguan Wan's mind that she'd receive such a huge and pleasant surprise. According to her initial plan, she had intended on making a move on only a handful of people after entering the Mystic Forest, for she would inevitably arouse suspicion if something happened to everyone.
Also, she could only act when she was certain that nobody would discover what she was up to. It was just like how she dealt with the dozen people when trapped in the enclosed area.