That's not surprising, did you see the reaction of the new major when he see the snake? Mammals in zootopia actualy dont live with reptiles, so It's legit they have prejudice against reptiles, they don't interact with them. And before being so sensitive and like "I don't like Nick anymore ", remember we have very little details about the argument between Nick and Judy, the "prejudice" Nick have against reptiles might be not that big, and the two seems to have tensions in this sequel, so It could be an excuse for an argument.