The headline keys on "racially offensive".  There is no evidence that the comments were made solely because the student was black.  Further there is no evidence that the black student is even a descendant of those subjected to the slave trade or is perhaps the product of modern immigration from an African nation.

While no question most people associate slavery with the North American slave trade - it is not beyond comprehension that the quip was made simply on the basis academic hierarchy rather than skin color.  In other words the remark could have just as easily been made to a student of another ethnic or racial background.

Surely an institution of higher learning and a graduate student at a leading university could take the time to determine if there was malice behind the remark or a pattern of similar conduct rather than simply seeking the safe harbor of political correctness.