I am no expect, but I've worked in an environment where software patents were a common place, so I have some idea about this. However, don't consider any of my words as fact, cos I aint no lawyer!
My first thoughts are there is no way that guy can sue you for copyright infringement. You're not copying anything of his. Copyright can be held for artistic works, such as images, music, or a written story. You cannot copyright the idea of a 2D space station game where you do x,y,z. I can happily rip off any game, so long as I don't steal any media, infringe any name trademarks (ie run too closely to its branding) or storylines etc.
As far as coding goes, you can patent software. If you develop something that is truly novel, and has never been done before (e.g. make a user interface interacts with a live cyborg monkey using a specific version of the TCP-IP cross monkey protocol) you can patent that. This then forbids anyone else from doing the same thing in software. However, if they can achieve the same results using another method, they're welcome to do that.
Again, I am no expect, but this is my understanding. So long as your media is unique, and the game in it's entirety can't be mistaken for the other game, you're all good. For example, I can make a cartoon about a mouse, but I could probably be sued if I called it Micky Mouse and drew it exactly like Mickey Mouse. That may mislead consumers and therefore is grounds for copyright infringement. However, if it looks a bit like Mickey Mouse, but not too much, and is called Bob Mouse, you're all good.
Insert piccy sig here. Eh? Why didn't that work?!?! Must ring help-a-noob. What was the number again? .... where am I?