Well, according to Cryptum (I'm fuzzy on details, haven't read the book myself) there was once interaction between humans and Forerunner. Maybe there is a whole civilization of people living among the Forerunner, who create a suit based on the one MC exits the tube with.
Like I said, I'm really hesitant about the game, but I'm really hoping that 343i proves themselves. I'm going to wait for more information before dismissing the game.