Is a short interview bad?

No, a short interview is not bad in and of itself. You should not base your interview's success on the interview's length. There are some great short interviews and some terrible long interviews. The only thing you can base how an interview went on is how you felt you did when answering questions.

If you felt that you were clear and successful during that short interview, that could be a great sign that the company feels they received enough information to assess you properly. Interview length does not always correspond with success, so do not let a short interview make you think it was bad, especially if that short interview felt like it went well.