Similarly, why have Lae'zel bother to call them "teethlings"? She thinks she's superior to everyone that isn't a gith - why is she singling tieflings out? (and with an insult that doesn't really make any sense - she's like a 7-year old calling names on the schoolyard).
I don't think that's meant as an insult. It's meant to show Lae'zel is unfamiliar with Faerun and its races and doesn't know the correct name for tieflings. She also says "Fay run" or something like that if you point out her mistake.
