While reading Maruyama Kugane's "Overlord" English translation, I encountered
"Is that so." in dialogues many times. Literally like this, without question mark.
-- There are many events in the arena, and sometimes adventurers end up fighting monsters. I’ve only met this person a few times, when I captured those monsters and shipped them here.
-- Is that so. Still, it ended up being quite useful indeed, so I must thank you for your connection. That said, what sort of monsters did you capture around the outskirts of E-Rantel?
So my questions are:
1. I guess that in this case the phrase was used like a rhetorical question. Am I right?
2. Is it allowed to use it like this in literary writing or was it just a non-conventional method of drawing the difference between the real question and the one that doesn't need the answer?