Also, I noticed the gnome won't give you the 10 if you discover it by orb, but then I seemed to find another one later. I guess the lore would be he gives you ten gold if you find his hiding place, and the orb is "cheating" so he doesn't give it to you and hides somewhere else
Actually, I'm pretty sure the gnome will always run to a random undiscovered tile if there are any left. Sometimes when you reveal an empty tile, you hear a higher pitched noise than usual. I noticed that the noise also always plays if you click a gnome revealed by an orb. I've also noticed that the gnome always seems to be the last empty tile I reveal. I think it's a reward for clearing pretty much the entire board.