While not all sites allow for guest to post new threads or replies, they should still show up in "recent activity" for those who do.
Member tab is viewable by guest and "recent activity" should count toward all recent activity made by everyone who post.Recent Activity is listed under the "Members" tab. So it should show your "Members Recent Activity". Guests are not members.
That would be my take.
Really think it should count for everyone.... I still see this as a design flaw (ergo bug).The phrase on the page says:
Activity stream for all registered members at XenForo Community.