I thought it was probably just that he had a carry permit for a state that had reciprocity with Illinois.
Then I checked and, while 21 other states honor Illinois permits, they don’t honor anyone else’s.
So - yur guesses are better than mine...
Illinois law allows for a CCW from another state, even without reciprocity, but only while you are in your vehicle or making a direct line to the trunk to secure the weapon before stepping away from the vehicle.
That may have played into the decision not to charge.