As far as why it was declined, It kinda looks like this is a crummy thing on Zone's end, I looked around on Zone and I myself never saw any of these rules that a head HAS to be human. Furthermore, Why would that be a rule anyway? You want to encourage your players to be more and more creative and unique with what they make, If someone want's to become a lemon head, Let them be a lemon head, It doesn't hurt anything. Not a single thing.
It's incidents like this where I don't need to question why Zone is so dead compared to other graal games.