A poster on Reddit managed to find the above while browsing the Xbox Store, and quickly grabbed a photograph. While the blurry nature and lack of confirmation from other sources suggest it could be a fake, the timing of it is consistent with what happened regarding Summer Loot Boxes, as is the description. It reveals some interesting things about Overwatch’s next special event.
Have a look at the second episode of Overwatch This, with similar speculation in this direction.
Most notably, an end date. Buried at the bottom of the listing it says that “Halloween loot boxes are available to purchase or earn in-game until 11/1/16 at 4pm pt.” according to a second post by photographer ChronosHero on Reddit.