I've participated in two group therapies, and both had screening. That was really to see if it's good fit, as your therapist said. They explained what the group is for, how they facilitate, and answered any questions I had. Then they asked me what my expectation to the group is and what I want to get from the group, and we confirmed that the group is right for me. The other things were basic questions - like suicidal thought, drug abuse record, drinking habit, etc. They use the word "screening," but I've never hard of anyone refused by it, unless you find you applied to totally wrong group and you don't want to attend. It's the place for you to learn about the group, and for the therapists to talk to attendees individually and find what kind of concerns each of them have.