Let me explain the way how package updating & upgrading works. Also, I'd like to cover distinguishes between them.
Updating is the procedure of fetching and comparing package lists. It can be initiated by this command:
sudo apt-get update
The APT application will get package lists, which contain information about packages available on download servers, their version and dependency information, and will determine which packages should be upgraded.
Upgrading is the procedure of actual changing installed packages. It can update, remove or install new packages. By default, for safety reasons, upgrade does only update:
sudo apt-get upgrade
but you can force it to make (un)installations:
sudo apt-get dist-upgrade
Just glance of these commands' output: the first will say that some packages will not be processed, and the second will make all the changes that should be made. For example, it will install new kernel image if it is available.
So, returning to your question, the 'updated x hours ago' message means that your package lists are updated, and there are not updates for installed packages. This is typical for LTS releases which are not frequently updated releases. They [almost] rarely receive security and stability updates. And for accomplishing the same thing that the GUI update manager does you should run in the terminal:
sudo apt-get update && sudo apt-get dist-upgrade