UnpackerBase.putUninstaller() creates an output stream for an uninstaller regardless of the uninstaller condition.
The Finish panel states the writing of an uninstaller based upon the existing output stream. The stream exists anyway and the message will be given regardless of the uninstaller condition.
Not until clicking the Finish button of the installer, the uninstaller condition will be checked in InstallerFrame.writeUninstallData(). If negative, no action will be performed (that's ok) but the uninstaller already exists (that is, a file Uninstaller/uninstaller.jar).
Besides, AutomatedInstaller.writeUninstallData() never checks the uninstaller condition.