A galley was a large-ish, primarily oar-powered ship.

However it also refers to the kitchen on certain even larger boats.

So, it's kind of ambiguous what GP meant - either picking a cook out of a galley-kitchen (who is not the best chef, but rather someone making huge amounts of food for a ship's crew), or picking a slave off of the oars in a galley-ship.

I don't know.