Is this something new? Because Pokemon games have been getting leaked weeks in advance for years now.
Maybe I'm misremembering, but Pokemon leaks are usually from Japan or Asia, aren't they? They tend to be cases of someone early in the supply/retail chain grabbing a copy, not a reviewer with an official code leaking it. Nintendo has much more control over the latter, and they do not like it when someone they have a business relationship with leaks something.