usually you'll see this type of thing a couple of weeks after the events end. They still have the boxes in loot tables in a few places in the system. Typically happens on non-Calypso planets, but sometimes on Caly too. (*it's just a trap to encourage you to buy keys off of the web shop in case you aren't already encouraged enough to do so - they only sell keys on shop in sets of 5 so they figure if they give you one box to top off what you already got maybe you'll throw some money at the webshop to top off since that little extra may get you one step closer to a set of 5*)