With the close-up on eye color and the structure of the story, the Warring Triad NPC is strongly hinted to be the 13th shard equivalent of one of Arbert's companions/best friend of said companion and not Ardbert (and thus carrying a fragment of Azem).

Well, not the Azem that most people mean when they say Azem. As for head-canons, considering that there can be multiple people running around with the Blessing of Light and Crystals and were throughout history, my theory is that some of them have shards of the previous Azem holders before Venat and 'our' Azem who had already joined the Lifestream.