If the gun was held
And the gun was tucked away
This tells us:
The gun brushed against a surface / a surface which may or may not have been a soft microfiber compressing surface
The gun was tucked away for some length of time (unspecified)
If that was a microfiber surface, synthetic or natural fiber or a surface with a fine animal hair finish any salt / sweat would be efficiently wiped and wicked away
The judge would have access to information about upholstery / interior of the vehicle / contents of the vehicle, The gun may have been tucked away in a discarded item of clothing. The gun may have been tucked away in a microfiber mitt (the kind you use to wipe your windshield / wash your car / buff your car / etc.
Most people drive around with things on the passenger seat, things in the car door, the glove compartment under the seat on the back seat, etc.
The driver of the vehicle wasn't driving real slow either, so if the gun was moving around it could absolutely have been shedding dna.
The article on page 1 is a very long read, but Its one of those where I don't think you can be exactly the same person before and after you make it to the end