Song Lan, Shanghai freshman, is dead already. Or not here; one going theory is that somehow he was over the weight limit. This would almost certainly have had to be deliberate sabotage, not accident, because the good enclaves have stunningly good scales and double-check, but it could have happened.
Other things that could have happened: he was ambushed on the way to the cafeteria either by a mal or by a student who thought it'd be a great opportunity to near-anonymously end up with an enclaver's entire welcome package. He had some kind of bizarre unprecedented magic interaction with the induction spell and got dumped in the void. Some student hid in his room in order to poach on the instant of arrival, maybe a senior who wasn't ready to graduate and figured they could pass themselves off as a freshman?? (This theory does not really make any sense.) He tripped and fell into a digester. He got turned around and trapped in a random classroom somewhere. He dropped his backpack into the void during induction and then killed himself in shame.