Many people install KDE applications without realizing it. Common ones are
Amarok, DigiKam, Kopete, Okular, Akregator and K3B. Some of these may come with
Ubuntu depending on how you got it and from what source.

Trust Update Manager.

If you really don't believe it, write down the name of one of them. Exit from
Update Manager and start Synaptic. Search for that name, and you will find that
it is installed.

Ubuntu uses GTK+, i.e. the Gnome environment while Kubuntu uses Qt3 or Qt4 for
the KDE environment - different window managers.

I you are using Gnome, unless you have loaded the kde-desktop package in order
to compile a KDE application that does not exist in Gnome, e.g. Tork, a Tor
controller similar, but better IMO to Vidalia, then you probably don't need any
KDE libraries.

On the other hand, if you have installed some packages that required KDE
libraries and have since been upgraded, and you decide to check as has been
advised, you don't need to write anything down. Just issue the following
commands:
1) cd /var/lib/dpkg/info
2) ls -1t *.list > ~ubuntu/Desktop/pkg.lists
This saves all of the packages you have installed in the Desktop file,
pkg.lists.

My understanding is that Linux helps a lot but linking to regular
updates of all programs it uses but you do not have to update if you do
not want to.

I suspect that either gambas or celestia (or both) are to
blame. I did not bother to find out, I just "froze" the version of the
kde libraries. Even if somebody is using them for something, I doubt
they are establishing a security threat.