The casual inaccurate statement like:-
it short circuited or something the moment it was plugged in,
does not cut it in electronics land. You are implying that a perfectly good Arduino was connected to a perfectly good Mac and the pair were damaged. That simply does not happen, period.
There must be something wrong with either piece or something wrong about what was connected to, or powering, the arduino.
Unfortunately you don't seem to be able to give any more information so I think this will remain a mystery as to who screwed up and how. But I will tell you that it wasn't the Arduino crew nor the Apple crew.
You said:-
and the macbook harddisk is permanently damaged
and before you said :-
and seeing a classmates macbook air + arduino literally dying after plugging in
The whole point about a Macbook Air is that it does not have a hard drive in it!!!!