I'm assuming that the assessors write down notes on how you've reacted and engaged in the group work. They could also do one on one interviews to get a better insight on candidates and they'll probably deduce from there.
As Nebs has explained really well, many recruiters take notes on what they see and hear from you during your group activities. They'll review these notes afterwards to match your performance against the competencies they're looking for. I hope this helps! 😄
