Sorry, I should have added some pointers to guide you better, it's a bit confusing right now. When you get to the "main" room you see an opening to the outside, so the robot says "There used to be a corridor there. Well, I guess you found a way down", meaning that you can go out of that door into some platforms that will lead you to the lower decks.
Later on the robot will ask you to go out, he means to go to the main door, which is the big circular red door near the spawn area. I should have written "Main Door" on top, or something like that.
Definitely navigation is a bit confusing at the moment, I'm sorry for that. I'll improve it once the rating period is over.