The war of the ancients was 10,000 years ago. How is Thrall at the end of the book getting news about Broxigar?
Time travel bs
The WotA novel trilogy has time travel as one of its main plot points.
So the first few chapters of the first book “The Well of Eternity” and the last few chapters of the third book “The Sundering” are set in the ‘present’. That being some time after the events of WC3.
Part of me thinks Blizzard did this whole time travel thing as a way to set up the infinite dragonflight and their connections to the Old Gods. As it was “The Old Gods” that created the time portal in the novels. Later sources would change that to being Murozond on the orders of the Old Gods. As Nozdormu heads off to investigate the origins of the time portal, which leads him to learning about his future self.
Just adding a bit more info to your explanation:
Thrall learned about Broxigar because Korialstrasz took on the visage of an old orc and entered Orgrimmar to tell him and give him Brox’s axe after Nozdormu returned him and Rhonin to the present time. Of note he also made sure Rhonin arrived just in time to witness the birth of his twin boys as well.
Krasus visits him in the Visage of an orc shaman and gives him the axe.