The Target thing is coming from the fact that there is an LRT scan gun in the background of one of the pictures. This is a popular item used for Target's inventory purposes.
That being said, Other companies like Lowe's, and distributors use those guns to keep track of inventory easier as well.
My theory on this is as follows. The leak did not come from a store, but from a distributor. I have a feeling that the new box set has been shipped to distributors this early so that they can get the product everywhere xwing is sold in time for a "on the shelves" date on September 4th. Having worked under a NDP (non-disclosure pact) before, his wording was in such a way that showed there were other products being produced that led to the delay of announced waves, and the new product was on the boat getting ready for delivery for a release date on force day. He did not make mention of how this product would "make waves" in the xwing game, which means the new core set is a stand alone game that is compatable with old set, but will include ships and upgrade cards that will make the age difference relivent.
TL:DR The core set will be on shelves (my theory) on september 4th at all places Xwing is sold. The leak is not specific to Target. Target might carry this product as it is a stand alone game; something they have no qualms in carrying.