It could be a drop from the boss in question, Kazzara, but could also be a drop from one of the end bosses, as it would thematically fit them. You can check the Aberrus boss list below, but it contain spoilers.
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Embers of Neltharion's first PTR build adds a new mount model that looks similar to the first raid boss from the Aberrus raid. This likely indicates that it will be a raid drop mount.