"The pointing finger is not the moon" has never, IME, been taken to make ontological claims of any kind about the moon, except that it's not the finger pointed at it. It means the same thing as, "The map is not the territory," and not, "Because this map shows rivers and towns in these locations, such rivers and towns must exist."

Your idea of a thing is simply and solely your idea of the thing; the thing, itself, is simply and solely the thing, itself. Buddhism just suggests out that you conflate them at your peril (to the extent, of course, that Buddhism has a notion of "peril").