I am setting up a situation where humans and goblins traditionally hate each other. I like to think Jazzle and Kettle eventually became friends and got over their prejudice, but I imagine it would be a point of contention going through the story. Goblins are a rarity inside of the city, and the few that are around are slave, illegal stowaways, or in rather rare cases secondary citizens. Outside of the city walls and the reach of authority they are more in control.

At least that's my head canon, I am open to talking it out.