Confused on Registration Code [PS3]

Before you say something, my code works and all this is more or less a simple question.

I Installed the game via Disc, and then used my registration code on the PSN (Assuming it would just give me a small key data so my product was registered) but seems like its another 6gb download.

So I'm a bit confused Do we have to install on the game disc THEN download another 6gb's for the Registration Code part?

I was hoping the manual would explain it better but sadly it hasn't so I have no idea if I'm just downloading another 6gb of something I just installed xD

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