Probably a dumb question, but how does this drm free stuff actually works? What is to legally stop me from putting up the file somewhere for everybody to download. I honestly never looked into what DRM free actually means, and since I buy my stuff and whish to promote that I never thought of it, but now that this game isn't available for sale at the moment I don't see a reason not to wonder.
DRM is stuff in software to control what people can do with it. DRM-free is without that. They can't control what you do with it through the software itself. That doesn't mean you're free to pirate it, because piracy is still illegal (depends on your country's laws, I guess) even without any DRM to try to stop you and even if it's not being sold anywhere anymore. Potentially, they could still go after you for that if you pirate it, but realistically, nothing would likely happen. Depending on who you ask, there may or may not be legitimate reasons to download copyrighted software. So it's up to you. Out of respect for GOG and the developers, I would say you shouldn't pirate it, though I would understand if you did.
And when it comes to dumb questions, why do I suddenly have '.280' behind my username?
There was a bug or something with GOG accounts a few months back where some usernames had numbers affixed to them. You'll have to contact support and ask them to change it for you.