No, the green sticks mean they are part of letter. So in this case it must only be A. The sticks turn black when the letter is found. But the game is to figure out in fewest sticks so you don't want to turn them black. You want to use you "negative" aka wrong sticks to help deduce things.
Yeah, just guess I'm a bit confused, because the green sticks I've chosen are valid for both A and F, so I'm not quite getting how F got ruled out in that instance.