Initially, it was just Freya coming to challenge him, saying she wanted to know how strong her future husband was, but then Ember decided to join as well, followed by Edward.
However, it didn't just start like that, Eleanor had said something which stirred their action.
"What if Ainz didn't use his full strength during the competition, because even if we had ganged up on him, we wouldn't win?"
Apparently, she thought Ainz didn't use his full strength during the test after watching his replayed fight against those magical beasts, her good instincts made her feel he was hiding his true strength, and if he had gone all out during the test he would have gotten more kill score.
Ainz didn't really know how she managed to come to such conclusions, but it had managed to stir the groups of students that had been accepted into the academy.
