I'm 100% sure it's just a wild guess! LOL

The point the writer was trying to make is that the players here are really good musicians, even though what they may play is very simple.
Most of these top session players in town can play all styles of music ... including jazz. Ever hear a Pedal Steel player rip off some Charlie Parker bebop lines? It's amazing really.
One guitarist that comes to mind is Glen Campbell ... who was the "first call" session guitarist here in Nashville for several decades, long before he started making his own records.
Another guitarist that comes to mind is my friend Tom Hemby, who is currently one of the top session players here in town. He mostly does the country sessions ... but if you go out to hear him play live with his band (they only peform once a month or so) ... he'll blow you away with his Jeff Beck, Lee Ritenour, George Benson, Joe Pass, etc., chops ... even playing fusion tunes from the likes of Weather Report.
So the point is that these session players can do FAR more than the are called upon to do in the studio ... which is why they are where they're at ... some of the TOP session musicians in the world.