That picture looks like it is at a distance of about 1 inch in model distance. The trick would be to make panel lines visible at one inch, when someone looks at it with a high power magnifier, but not see the lines when they look at it from twenty or thirty inches.
We need to consider scale viewing distance. To determine this, take a common viewing distance and divide by the scale. So twenty inch viewing distance at 1/72 scale is 120 feet.
But you can see panels on bare metal finishes because of different alloys on different panels, or different mill finishes, including which way the sheet that makes up the panel came through the mill rollers. So different panel appearances on bm panels is different than on painted aircraft.