I've seen this before. I was involved in one where the winning team had been working for months beforehand (their website was registered > 6mo before the event), had prepared presentation materials far before the event including design mockups, and presented with nothing more than a pre-cooked video that was looked manipulated to show "working" code. None of us knew for sure, but it looked like they had just built st…
So, did anyone complain at the event? Or even after the event? How did the judges and organisers respond to the complaints?
The strongest complaint we could make was that it was strongly against the spirit of a hackathon, which is a difficult argument to win.