Yes, it is all Sirius' doing. He posted in the Sett that one could earn Diamonds by going into the rooms of other Houses and posting a Holiday Greeting! click
No box of explosions in here for you, though. Didn't find one with pretty blue stones. Oh Well!
I hope for all of you a wonderful holiday season in your room wide and circular and airier than any Harry had ever seen at Hogwarts.
