Perhaps it could have something to do with easter eggs in vanilla hearthstone? To tie it back to classic's release? I found a page online that has a list of them and a large few are in the Barrens. One specifically caught my eye talking about a poison rogue quest in the game that I figured could be related to poison rogue barrens set cards. http://www.blizzardguides.com/wow_cool_easter_eggs.html
I mentioned this to somebody on twitter, but I'll drop it here too in case it's in any way helpful:
The card back is Kael'Thas themed. The 3 green orbs, the red and gold, down to the name in the files. Kael'Thas is a fella who loves the number 3, apparently. So my first guess would be doing things in 3's, or doing 3 different things.
Also, since it's Kael'Thas themed and he was from the Outland set, this might have to start on the Outland board.
Usually the text that its on the side of the card when you select it its funny or ironic but in the case of Xyrella, Varden Dawngrasp, Cariel Roame and Tamsin Roame it seems to be some sort of lore, anyone can relate that text with something?
it is because its fanmade and not done by blizzard :D
jokes for blizzard aside, seriously tho: you should see the cardbacks submitted to that competition. There are like 100 of them and almost all of them are very, very good. Like, most of them are better than 90% of the cardbacks in the hearthstone right now in my opinion.