Don't feel like a slacker. Different people already have different skill sets and different previous experiences that can help.
Example. Over the last few years, I've gotten into running. I ran a half marathon a year and a half ago. There were about 3000 people in the race. I knew there was no way I was going to win. There was also no way I was going to win my age/gender division. But I wasn't running the race to beat everybody else. I was in the race to compete against myself. I had set a goal to finish the thing in under 2 hours, and made it in about 1:58. I accomplished everything I set out to do, and I was incredibly happy about that. I don't really care that somebody else who probably spends a dozen hours running every week beat me. I had accomplished my goal, and the reality is, I did something very few people in the world ever do. The fact that you're even making a game (and already made at least the one a few months ago) put you in a league that many professional software developers only dream about.
Another thing that should be said is this. You've looked at this other guy's source code; I have not. But sometimes, rushing to get something done quickly means sacrificing quality. It is clear from your posts here that you are building at least certain pieces that are reusable, and you're putting a lot of thought into that. That's a great move, even if it comes at the cost of taking longer to do things.
So anyway… don't sell yourself short. You're doing a great job with these games. Far better than most programmers. Just enjoy the ride, and learn from others around you who are doing similar things.
By the way, what you're describing (another person who did the same game as you in a very short amount of time) is one of the reasons why this little competition that we're talking about should be treated really casually. Everybody who participates will have different skills, available time, and backgrounds. It isn't going to be possible to fairly pick winners under these conditions. I think the way we'll all get the most out of it is in knowing that, "Hey, I gotta get some work done on this, because everyone else in the competition posted an update today. I need something to show too!" And then at the end, we can share experiences and talk about what good decisions we made, and what bad decisions we made, etc. I think that's where the real value in doing the competition will be.