Yes, that is a negative.

Student: “Teacher, we have class today?”
Me: “No.”
Student: “We have class?”
Me: “We don’t have class today.”
Student: “Oh? We don’t have class today?”
Me: “No.”
Student: “Uh? We HAVE class today?”
Me: “No, we don’t have class today.”
Confused Student: “No class?”
Me: “No class.”
Still a little confused Student: “OK. Bye Bye.”

Only after she left did I realize that this was what I had learned last week. See, in Korean, in a situation like this “Yes” will mean something like, “Yes, I agree with you and what you are saying is true.” It amounts to basically saying the opposite of what you would normally want to say in English. A better answer from me would have been…

Student: “Teacher, we have no class today?”
Me: ”Yes” (That is correct. We have no class today.)