See post #37. It is far easier to ignite primers in certain conditions than you might suspect.
Having handled millions of primers without accidental ignition, I will go with my long experience. The chain here is accidental ignition of a primer from luggage handling on a tarmac. A very unlikely event being heard by a luggage handler with jets at idle, equipment being used, planes landing and taking off?
The unlikely becomes absurd.
For what it is worth, TSA refs and every airline policy forbids transporting primers and black powder. It is even possible that he was using an old muzzleloader trick of using shotgun shells (which are legal to transport with declaration) to hide his primers. But this whole story of a primer going off in luggage on the ground and being heard is increadibly unlikely.