HI @Katherine1212 it's difficult to provide accurate feedback without seeing the listing you are speaking about. Typically, an ad for a shared space will read as "room in XYZ locations" whereas an ad for an entire space will read as "apartment, guest suite or home in XYZ area." It can be confusing at times to discern what is what.
That being said, if in fact the listing was accurately described, the host has a right to uphold their cancellation policy which your son agreed to when booking. You can go back to the listing to review that policy. If the listing was inaccurate (i.e advertised as an entire home vs a shared space) then you have grounds to argue for a penalty free cancellation and full refund.
I would review the listing carefully and contact airbnb for further support