If Hireshmont doesn't get what he wants in this affair, it'll be the first time he's ever lost: at anything, ever. He isn't used to losing.
Meh, everyone has to lose every now and then.
Plus, there's a huge culture gap.
Oh, definitely.
For Hireshmont, not commenting on the exact details of a treaty is pure animalistic barbarism.
But as Brance demonstrated, Hireshmont never actually proposed a treaty. He stated the goals he would like achieve during the treaty negotiation. i.e. "We would like to come up with a treaty that covers the following points", not "We would like to propose the following treaty". A subtle, perhaps, but substantial difference. Even the wording of the points provided was completely unlike anything I've ever seen in a treaty, and bore no resemblance at all to the treaty Terran signed with Asylon. Then when Hireshmont actually did send it as a true proposal, the first sentence of his message was "You lie.", and then he continued to attempt to embarrass and insult Brance. At that point, Brance had no intention of even discussing the matter with the rude Terrans.
As far as he concerned, we are separated from the monsters by our ability to write complex legal documents. Thus, Brance's arguments are pissing him off.... because Hireshmont has always argued in Terran for friendly ties with Astroist and a very moderate stance towards Astroism, based on the fact that they were decent, civilized realms, sharing the goal of pacifying the wilds... but this conflict is causing an existential crisis for Hireshmont as he wonders if Astroists are actually humans, because they seem incapable of negotiating a treaty, which means, obviously, they're not actually humans.
Brance is mad at Hireshmont because, from Brance's viewpoint, Terran stuck its nose in where it didn't belong, claiming lands it had no business claiming, and declaring that the whole thing was "a done deal, and please kindly refrain from taking our land, thankyouverymuch!" Then when "negotiations" started, Terran approached with a proposal where, essentially, everything in it was non-negotiable, and refused Brance's request that all the disputed territories remained untaken, whereas Hireshmont declared that Terran would take one region, and Astrum would take none. There was, literally, no room at all in the agreement for which Brance could negotiate.
From there, it only got worse and worse. I'm pretty sure that everything Brance and Hireshmont said to each other pissed the other one off. The whole thing was quite interesting. I'm sure that at some time in the future, this whole mess will come back and haunt everyone.
