I thought about that semantics which you are referring to. But then I thought, what all we can search for, comes under nodes, be it a discussion thread or a page. Do we have anything else to search (other than members, which is not included in this search page anyway)? If my above argument is right then I would add, even the result page related directly to the that same space. In my opinion, it was just a clever utilization of a free space to provide additional navigation options. But of course XenForo team has better experience about web user experience.