I was thinking moonfish as two different things, the first being the Moon, obviously, but the second as a "hockey fish", playing up the playing surface as an icefloor. I first heard this term in a book
"The Shockwave River", an interesting SF novel from 1975 that predicts many things, including how intertwined the internet will be with people. Strangely, not via computers but touchkey desk phones with a screen.
I haven't been able to track down what is a "hockey fish" -- in the novel it is referred as a "hockey 'fish" and seems to be someone who follows a particular hockey team. It could be a current term in the hockey world, or just a very obscure reference the GDC came up with.
In the novel it came along with "sweedack", which I also thought was a current hockey term, but one internet source says it was also created in the book -- a French contraction of 'je suis d'accord' used by French-Canadian hockey players in the novel.