A bit of Googling suggests that it was THIS actual Jump-Jupm Chess that I got sent: http://community.livejournal.com/pokemon/2928629.html. It has the same sticker on it. And according to that person's eBay feedback, someone with the username of irfon bought a Jump-Jupm Chess & got given feedback on 25th August... (Worrying how easy it is to get around eBay's "anonymous user IDs" on the bidding page). I know someone called Irfon, but I've never seen him use that as a username.
It's just the whole mystery of having a parcel sent sea/surface mail and it taking 6 weeks to arrive, without being contacted by the sender to say "hey, I've sent you something random". And it is very random! I have honestly spent all my spare time today asking people if they sent it to me, and I'm extremely amused. Hehe.
Also, I'm going to have to take it on the next Pokecharms meet and inflict it on everyone else.