I looked at some of the winning entries and noticed that there was a lot of HDR shots.
I looked at yours and figured you probably used it too on some of your shots. From your description of how you worked it sounds like you used what might generally be called faux HDR. Not a bad thing at all, in fact it's a good technique and I like it.
HDR is interesting because you can make it look natural but people tend to give their shots that special look that shouts "HDR", I'd describe it as a kind of SciFi fantasy art effect I guess. It can be quite pleasing and give interesting results but I do tire of it when I see it all the time. Your technique, and some of the winning entries, is of the more subtle variety.