The Grotto Netherwing Drake was originally the Traveler's Log reward for the Trading Post in the month of July/23. Back when it was first released in the Trading Post, customizations were datamined for the mount and eventually added in Patch 10.2.
If you missed the Trading Post reward back in July, you no longer need to worry! Another source for the mount has been added in Guardians of the Dream — You can obtain it from the Wrathion and Vyranoth Questline in Patch 10.2, specifically from the quest Dragon Keeping.
If you have previously obtained the mount through the Trading Post, the mount reward will not show up.
Screenshot taken from the r/WoW subreddit. Thanks!