How was it bad that they sent him home? A spy is a spy. In China they would have just killed him or imprisoned him if a student were sending information "back home." If you don't believe me that China simply kills spies, look at the spy purges in the Obama years after a breach in the CIA's communications.
Reread their post. They said their action was bad enough for them to be sent home. Not that it was a bad decision for them to be sent home.
I have read enough spy novels to become convinced that both sides just send each other lies and siphon off their budgets for personal luxuries.
But not bad enough that they could resist the pressure to have him back with just an excuse of "oopsies".
It's bad because MIT reprimanded him for "scrap[ing] every piece of internal data and code in the lab and sent it back home"? That's felonious territory. He should have been deported indefinitely.