That would just get the person viewing the page, not the person who made the post.
For threads, it looks like you can override XenForo_ViewPublic_Thread_View and swap out the XenForo_ViewPublic_Helper_Message stuff for your own code. $this->_params['posts'] should contain all the message data that you'd need. Other areas like private conversations, signature/post preview, etc. may have to be looked into the same way.