This happened to me a few weeks back. I found a random “Spectral Mawrat’s Tail” in my bags. I thought it was a Renown/Covenant mount; WoWhead said it’s a 0.06% mount (not sure if drop rate accurate).
Needless to say, I got Flametalon a day or two after learning Mawrat’s Tail and Ashes of Al’ar a week after that. Pretty successful mount week that was.