Not sure whether it's lost in translation or something else, but yeah I also found it to not make sense (maybe ending the war in peace = betrayal? It's quite a big leap of logic if that's the case)
The fact that it's also written as if the merchant found out Maou's identity was also weird.
I talked with chat GPT for this chapter a while back hahahaha, it was really interesting discovering our history paralel to this series.
Here's a very short TLDR from what I learned.
There was a time when . . . . Wars were used as the engine of a society, an economic driver. Proposing other methods mean threatening the current society itself or humanity for this series (since its a war between humanity and demons).
Merchant doesnt know Maou's identity. But as a very important person in businesses he has to be
REALLY GOOD at reading people. When the humanity itself is depending on war as the society engine, Wouldnt hearing someone says otherwise raise suspicion?
This series is pretty chewy, but when finally swallowed with some learning. Its really great.