Constitutional Rights for Guantanamo Bay

I don't fully get it, but apparantly prisoners held in Guantanamo Bay now legally have Constitutional rights. I understand if an American citizen is held in Guantanamo Bay, but how does a non-citizen have the rights of a citizen? I'm not a big fan of the idea of torture, but I always thought that the rights of an American citizen both apply only in America and only to American citizens.