I got Portal for free???

The gaming gods smile upon you!

What do you mean by "somehow"?

You can click on your name from the top right of your Steam browser and see everything that happened to your account.

Yeah but I somehow just got it today for some reason. It's always been in my steam library but that was only the demo.
Now it's changed into the full one for no reason ever since today.

It was part of the preorder for Portal 2....
Edit: I apparently can't read..... :D

Have a look at: https://store.steampowered.com/account

It should tell you when you got the game, and whether you bought it, it was complimentary (free from Valve) or a gift.

Did you win Grand Prize?

EDIT: nvm, i dint see portal in ur wishlist

You may see this "Portal - Complimentary (Opt In)" on your account if you got it free before 24 May 2010, like me.

Thanks RJ, I found out I got it complimentary from Opting in something.