Only group members in private and secret groups like the HHA Facebook group will see any posts or comments made in those groups. Even if you are tagged in a post/comment within the group, only group members will see it. If you happen to see posts from such groups in your Home News Feed, these will only appear in the News Feed of group members. The only way for one of your friends to see a post or comment you make in the group is for that friend to also be a member of the group.