Because he obviously got the airborne disease from someone else and is therefore got it from someone else and is considered "exposed" and should be treated so
If the disease is communicable, it is contagious. If it is airborne, it is transferred through the air, as opposed to physical touch or blood-borne. Being in a confined space, such as an ambulance, with an airborne communicable disease means you have most definitely been exposed to it.
You could either have Tonsillitis or something else, worse or not. Tonsillitis is usually caused by a viral infection but can be from a bacterial infection.
