The September is the last "showcase" demo, which mostly consists of just animations and not much more. In that regard it is a bigger game. But the latest version of the game, the one linked above that, has a sort of beginning of a quest, and then a bunch of animations between just the PC and NPC. Because the September build has a bunch more character models, it makes sense that it is larger in size. Besides, the size of a game on disk says relatively little of the content and quality. It could be that they optimized a bunch of stuff in the meantime to reduce overall disk usage.