It's most likely something embedded in the file, though some car audio units can intelligently "strip" numerals and file extensions from file names.
If you have a tag editor program (I personally recommend one called "TagScanner" which you can download FREE)
you can read the meta data that is "embedded" in the files on your mp3dvd
You won't be able to change any of that data (on the DVD),
but TagScanner5.0 will let you read it all and edit/add tags
to any mp3's that are on your computer.