That's pretty bad. Interviewing should also be about selling the candidate on the company. If they get an offer you want them to accept. If they don't then you don't want them bad mouthing you to other potential candidates.
If an interviewer insulted me or my language choice in an interview it would definitely make me wonder how they would treat me as a coworker.
If an interviewer insulted me or my language choice in an interview it would definitely make me wonder how they would treat me as a coworker.