Rogue class mount assasinations

So...I was doing the assassinations and was in the stormwind auction house finishing it up. I didn't bother to really read anything and just saw a red name. Popped CDs, killed, sprinted out, vanished. Hearthed back and went to turn it in and it said I still had a target in Stormwind to kill.I had one shot some level 20 noob who had been the only person flagged in the whole place.