They could be using multiple tab browsing, or going to the pages via their browser history / bookmarks. If your URLs are simple, they may be advanced users who are just typing in the URL, or they may be using URLs in their paste buffer.
Or they may simply be going to the "hub" and quickly clicking to go to the other page before the "hub" has a chance to track the page view.
There are many ways to navigate websites, and they aren't always the path that the site owners intended or expect..