So you're studying sports science, are you?

(Grammar Questions I Couldn't Answer)

With apologies, another question about question tags.

This sentence comes from Complete IELTS 6.5-75, Unit 3, Listening p.30-31.

There was a sentence in the transcript that a student had a question about:

"So you're studying sports science, are you?"

"Shouldn't it be a negative question tag?" a student asked.

In ESL, we teach the students that positive sentences have negative question tags, and negative sentences have positive question tags.

So for example:

"You're a student, aren't you?"
"You're not a doctor, are you?"

And yet, here was a sentence that violated this rule.

My first thought was that maybe I had transcribed it wrong.  But I double checked the recording, and this was indeed what was on the CD.
And furthermore, to my native-speaker ear, it didn't sound particularly wrong.
And yet, it violated the grammar rule that the students had been taught.
So I just told him I didn't know.