Gigers original space jockey idea

He also states: H R Giger : As for the chair in which he sits, I thought it had to be mechanical but not with normal arms and legs that could be moved with the feet or the hands. I liked very much the stone tablet in 2001 Space Odyssey, because it seemed to have some interior-like computer. So I thought that the outside could be very normal-looking and the whole machinery could go inside. (FX, 7, 1999 (spanish magazine) )

Giger has so many thoughts and ideas in his head that he could write or collaborate with someone to write a totally creepy sci-fi movie.

Totally. But here's what Ridley says: Ridley Scott: "As they enter the derelict, I wanted them to come up over the edge of something and into this vast chamber that's dominated by a huge chair. In preparing this frame of the storyboard, I went through Giger's Necronomicon and took this character, whom we call the "space jockey", because I wanted a fossil, almost, one which you'd have a hard time deciding where he leaves off and the chair, on which he died, begins. So here they are with this dead space jockey frozen in death to the weapon he was firing when he died. And he's kind of gargoyle-like and spooky. Sometimes we got very close to the films visuals in the storyboard" (Fantastic Film, number 11 (US), p 28-29) Hmmm... weapon?

they seemed to be unable to decide what that thing was that the Jockey was sitting at.

grown out of the chair is way more alien-esque, biomechanical and in keeping with the body-horror theme than the relatively pedestrian "SJ=suit" idea. Imagine the ship has its mission programmed through the consciousness of a pilot, a biomechanical computer, that just happens to retain arms because they're like "legacy source code", necessary for the ship's hybrid intelligence to have "compiled" (grown) correctly. (see modern theories on AI that state human intelligence is highly tied to the IO, including the tool-making hands)