If you reread the article carefully you'll notice that they RE-COOKED pre-made stock to make the comparison.....why they would do that, I have NO idea....it doesn't make any sense!!!!
"I took 4 liters of conventional chicken stock from the restaurant and pressure-cooked half while the other half simmered on the stove. This time, I didn’t use the school’s pressure cooker, I used my own. When I compared the two stocks side by side the pressure cooked one was far browner. I hadn’t thought the pressure cooker would change the color of a pre-made stock. When we tasted them the pressure-cooker won! Finally.
I then ran the same test with the school’s pressure cooker and the pressure cooker lost. WTF?"
I've compared the stock produced by a "non-venting" and a venting pressure cooker operated just below the point of venting...there's no appreciable difference in the two...they're the same.
If you really want to capture ALL the flavor, make the stock in sealed canning jars inside a pressure cooker/canner.