The rule about including a notice regarding the contest sponsorship in your credits should have been included in the original announcement, yes. In principle I agree that it's problematic that this wasn't made clear upfront.
It is sometimes difficult to find sponsors for contests like these, and I imagine it was a requirement for these particular sponsors. There are a lot of things to consider when writing up announcements for a contest, and sometimes what doesn't seem like a big deal to the contest runner is a bigger issue to some of the entrants, that's understandable.
Nevertheless, I'm consistently disappointed by this community's behavior when there are contests. People volunteer to run contests on this site out of a desire to contribute, do something fun for other people, and even goes to the trouble of getting a sponsor to provide prizes, and all some of you can do is complain. Nobody running any contest owes you anything.
Anyhow, I'm excited to see what comes of this contest, though unfortunately I don't have the time or equipment at hand to make an entry myself. Good look to everybody participating!
