Academic Freedom for students re: advisors and solo papers?
Going back to Wikipedia's source, we're told that


  Strominger has since moved Pasterski, as a second year graduate student, into “Mode 2,” where she is given the latitude to work without his direct supervision on any topic of her choosing with anyone she wishes. 


In other words, Pasterski seems to have quite a bit of independence to choose the direction of her work and collaborators. I suppose this represents academic freedom in the sense of "freedom of inquiry", but as far as I can tell neither "mode 2" or "given academic freedom" are formal designations at Harvard. As such I suspect they are not associated with the kind of protections that the academic freedom of professors can have (i.e. tenure). That is, in this case, it appears to be an agreement between advisor and student on how to handle things.

Since the original source calls it "mode 2" it seems likely that the phrase "given her academic freedom" is just a turn of phrase in the Wikipedia page. After all, freedoms are generally not granted by or from an individual. The notion of student academic freedom is generally defined in policies that would apply to all, not as a prize to be won for jumping a hurdle. Of course, I cannot prove a negative, so the latter might still happen somewhere.