Yeah, the novel gives a lot more of insight. That's the real challenge for the webcomic to face. I also think that the "translation" factor can also be part of the reason. I don't speak korean so idk how it was said in the original language, but a lot can be lost in the translation.
They came there to ask him a favor knowing they can offer him nothing. That is basically asking for someone's pity. He just went ahead and gave them more than they wanted for the same reason. I don't think it's insulting at all.
If they had intended to trade his favor for something of value to him but got slapped with the pity reason then yes it's insulting but they were asking for pity and got it. Can't complain about that and I don't think it makes them stupid if they're doing this for survival. I think thr reason they also took a liking to him is because he didn't sugarcoat it. They would've been more insulted if he thought they were idiots and gave then another silly reason.
I hope Taylor and Cage get their own pov. When I read the 30th chapter, they looked kinda stupid for taking a liking to Cale despite him "insulting" them with the pity and not taking the vow thing (from my perspective, at least). I had to read the novel because my brother told me it would answer all my questions since the writing style is from a third person's point of view.