I can't seem to find any information whether Oracle Linux comes with pre-installed Oracle-DB or not.
It does not come pre-installed. Oracle Linux is just an operating system - specifically a clone/derivative of Red Hat Linux - suitable for many uses and not just as a database server. It does come with certain kernel tweaks meant to make it a better database server should you choose to use it for that, and with available RPM packages to help you pre-configure the server for database installation, but not with an actual installed database instance.