I'm sorry but the game was not "ported" to the Amiga. This is completely wrong. It was made and designed on the Amiga by Eric Chahi himself. The PC version is a port. I know because I got the Amiga version right when it was out back in the days and it was the first one, plus I watched numerous documentaries showing Chahi working on his Amiga when making the game.
So if you want to look at the original source code (or at least understand how it may have worked) it would be wiser to decompile the Amiga binaries.
Since the game itself runs inside a custom designed virtual machine, are not all versions "ports"?
The amazing thing is that he targeted multiple platforms right from the get-go in a particularly elegant way and didn't let that turn into a multi-year yak-shaving "game platform" exercise.
How can you be sure this was the original design if you do not check the Amiga sources ? As far as I know he did not develop all the other ports by himself - and I distinctly remember that the Megadrive and SNES ports took a LONG time to appear.
Eric Chahi's article about the game's architecture (linked to from the article) shows that the original Amiga version uses the same virtual machine architecture as the version that Fabien Sanglard dissects. The game was designed from the ground up to be easily ported.
I think you can find a couple on youtube... and I have one I taped back in the days on VHS, but it is nowhere online as far as I know. Plus there was a whole TV program about him (at least a good chunk of it) back in the early 90s with extensive interviews. But I have never got a copy of that one.
When I first saw Another World, the animation was so incredible (for the time) that I figured it was one of those newfangled CD-ROM games. Then I bought a copy and was shocked that the whole thing fit on a single 1.2MB floppy -- most graphics-heavy games (like Wing Commander) shipped on several floppies before CD-ROM became prevalent.
I always wondered about the tiny executable, too. I think I just figured that it was a stub that loaded an overlay from the big data file. Guess I was wrong!
On the other hand, as a kid I was amazed by Sylpheed (megacd version) and always thought that it was 3d/vector graphics when in fact most of the visuals were pre-rendered videos (leveraging CD-ROM capacity obviously).
This is one of my all time favorite games, and it tickles me to my core that 1) the programming is apparently as brilliant as the visual storytelling, and 2) I had an idea like this some time ago and now I'm wondering if I shouldn't dust it off ...
So if you want to look at the original source code (or at least understand how it may have worked) it would be wiser to decompile the Amiga binaries.