If you try and install a CB Plugin using the Joomla installer you will see a message similar to: "JInstaller: :Install: Cannot find Joomla XML setup file"
This message is generated by Joomla and it tells you that the package you are trying to install via the Joomla installer does not have a Joomla XML file in it. Of course it doesn't, as it is not a Joomla package. It is a CB Plugin package that needs to be installed using the CB Plugin Manager.