you should make screen capture or evidence (just like VOTING POOL, Chat or anything else) in order to proof that the winner is true choise from DEV Team.. the question, why need evidence? Because only 1 winner, no 2nd or 3rd winner.. so all contestant will accept gracefully and feel fairness for this contest..
This is definitely not necessary. OP obviously represents Coinbox, and speaks in the name of the team. If you don't trust him, why should you trust any evidence he presents as that can be easily fabricated?
They escrowed the funds as suggested, chose the winner and that's about it. By the way I liked your design, imho it was almost as good as @Jayce's submission, but that's how it goes with these contest.
Btw, congrats to winner!