It's most likely a picture of the Autumn War, which was well pre-Calamity. I think in the picture there looks to be a Chocobo. Which may make it a picture of Beltrant Durendaire and his chocobo Ouranos.

And yeah it's weird, that NPC has a special robe. He's a Thaumaturge and in Gridanian territory, most "warriors" in the area are Lancers or Archers. Louisoix would have been Ahldbhar's Master...course this is just me hopping lol