That is a PbP habit. I squeeze as much as I can into a single post. In abstract it can be seen as half the conversation. There would be some back and forth, but if we posted a literal back and forth it could take days or weeks of real-time to hold a short conversation.
To be fair, that is not what he said. The position is Sergeant, as in "Turb Sergeant", a position befitting a Grog. Though some in-character confusion of terms is plausible. Roberto's mundane military experience was as part of an infantry mercenary company. From my research (a few years back), I discovered that modern military ranks are evolved directly from mercenary traditions of the middle ages. Mateu is not a green recruit, he is a veteran. He comes off that way at least. It doesn't seem likely that the Order of Saint John would send their lowest ranking man as a solo operating emissary. At least worthy of being a Lance Corporal if not a Sergeant. Presuming you have seen combat.
Which again makes me think that Mateu is unlikely grog material. It isn't the stats, it is the backstory and the way he is acted out with bold confidence. However, it may well be that he is a patsy or a drone. A plant. A man on the inside for when the real diplomat shows up. Your Order doesn't expect results from you, and you have no strong contacts to communicate with them. You are a canary. They sent you to test the waters, and if after a year these devil-wizards haven't eaten you, it is safe to send visitors of rank.