the fact that kobolds seem to be this more "animalistic" race, with kuro talking in broken language and like improper grammar. this, coupled with the fact that he seems unaware of the fact that he's being exploited by mick, makes kobolds appear to be less intelligent than other races.
but we actually find out that the simple speech patterns are in fact due to common being kuro's second language. and in a scene where kabru talks to kuro in his native language, it's actually kabru with the simple speech patterns.
we even learn that kuro seems to actually have a much better understanding of his situation with mick than we first imagine. merely wanting to stay with them so they can have someone who they can feel relaxed around.
this, coupled with a bunch of other things, really makes dungeon meshi stand out from other fantasy media. there are no "dumb" or "evil" races, they're all just people.