No, a group thread wouldn't be, not for everyone. A group thread counts for the person organizing it, IE, you can make AC by providing a post to mingle. So the players bringing this up have a valid concern. Also, even in the case of mingling posts, the post would have to be open to count, so the detective post in my case wouldn't, but movie night, which was open to everyone, would be.

The terms for that are strict enough to encourage more open posts for them to count at all, but don't take into account folks tagging into a mingling thread rather than throwing it, so I can see the concern the players have with this.