i said i understood sequels, but why name the first game something like that?
As I stated above, it's not always that there will be sequels, but that there may be plans for other parts in a series, which could include parallel games. Not all plans fall through, but it's reason enough for the title. Also, again, sometimes it's just a subtitle to add effect.
Example: Harry Potter. The author planned on writing more than one book, so she gave the first one a subtitle as well, instead of just going "Harry Potter", "Harry Potter 2", etc.