I know Wikipedia is not the best source in the world, but when it comes to definition of Portable Applications, they are right on the money.
A portable application does not leave its files or settings on the host computer. Typically this means that the application does not write to the Windows registry or store its configuration files (such as an INI file) in the user's profile; instead, it stores its configuration files in the program's directory.
Source:
So in order for a non-trial(licensed) "portable" installation of DVDFab to run on a PC, it has to "talk" to the registry of the host computer thus making it a non-portable application. Methinks.