I have just double-checked this quest, in Aureus his dialog there should be an option to say :
-"Let's discuss these expeditions into hostile territory you mentioned."
-"So, about these burial grounds..."
After you have completed the escort, this should fully complete the quest when bringing up the topic to Aureus.
Exactly.
I had the same problem yesterday.
Perhaps the game should highlight dialog in white for those you haven't asked and in light gray for what you already talked about.
But when the Quest Log says: "Go talk to NPC XYZ", simply trigger all dialog options.