Apparently today, one of my friends, who has only played about 30 games total, and never got past 1550 got gladiator, duelist, rival, and challenger achievements, and no one else have these yet, not sure what actually caused this, but I'm pretty sure it belongs here, here's his armory for proof
The World of Warcraft Armory
Notice how he doesn't have any "Just the two of us" etc at 1550 even.