You were still right that they should have not spent so much of the group time talking about the activities they did together outside the group whether it actually did hurt those not involved or not. The group needed to focus on the topics for ALL in that group.

My DBT group got together to see a movie. I actually went to see the movie alone because I couldnt get together at the time the few of them went...we discussed the movie in group because it was a group topic about the mind.....we also have a few that get together outside of group but I am so busy with so many other activities many times I don't participate. But our group leader kept us focused on topics that were helpful for the whole group. You are right. It is the facilitators jobs to keep the group focused on EVERYONE not just a subgroup of the people involved.