config.php is not a configuration file, you are not meant to edit any aspect of this.
config2.php is the configuration file, you are meant to edit this.
After looking at both of these files I soon realised why they existed in this way.
At one point config.php contained some configuration settings, but they appear to have moved into config2.php.
I'm proposing that config2.php should be renamed to something like "settings.php" in future versions making it easier to identify.
It seems the only place that config2.php is included is is in config.php anyway, so it would be easy to make this transition.