I do know the reason for it being Goonies II and not 1 though. The first Goonies game was released on the Famicom system (japanese nintendo) and for whatever reason it never made it to the U.S. It actually works out good though because the game has nothing to do with the movie storyline and it takes place after the movie. So calling it Goonies II kinda makes it the next and finall chapter in the Goonies story.
So if you itching to play the first Goonies there are a few things you can do about it.
1. Go buy a Famicom system and the Famicom Goonies 1 and hope you don't need to understand japanese to play.
2. Look around for the rom.
(there was an american version pirate of Goonies that had sold on ebay for about $100 bucks but it turns out it was just a fake)