Translation:You are not a student.
Breaking this down for those who arent aware, 是 means a few things: - Yes/right (affirmative response) - being/to be (verb) So you can use it in a few ways, like 我是吃饭 to mean "I am eating rice" OR 是的 to mean "yes it is"
Thanks but I was wondering isnt 不 a negative too ? Why would we also need to use 是 ?
Seems like the answer is treating "aren't" as a typo (for "are not"), so letting people know and reporting it.