Posting dupes is generally considered ok on HN if the link is relevant but the previous post didn't get noticed. (Sometimes the mods will even email you asking to repost a link.)

In this case, the interest in the 1k intro winner makes it likely that people might want to see the demo compo winner too, so IMO the repost is warranted.

No, not really. The submission you linked to never got any attention. A small number of reposts are allowed if a story hasn't gotten significant attention in the last year. See here:

https://news.ycombinator.com/newsfaq.html