I think this is SORT OF correct.

You want to pick an area that is the closest to neutral object available in your image. You don't want to pick an area that is definitely not truly neutral--for instance, a section of concrete or rock that really has a beige tone rather than a true gray.

But often there are neutral-colored objects--- a gray rock, a white shirt---that do not appear in the photo to be neutral, because they have, for instance, a very blue cast due to very cool lighting. In those cases the blue value (for example) would be significantly higher than the red or green values, and the color temperature would be adjusted significantly upward to compensate. You might not be able to FIND a point that shows the RGB values almost the same. But the neutral objects would be the closest available to neutral, and would be the right points to use for your WB correction.

Sometimes it's difficult to judge. I've picked objects I thought were very good to use, only to have the WB look awful when adjusted. In that case I will use the slider until it looks "right" and then set other photos in the same lighting to the same color temp.

The BEST solution is to use a neutral card. Include one in a test photo for every lighting change. It only takes a second.

I used to use an Expodisk. They work well IF you have single source light and can point the lens toward the light source. They do not work really well with multiple light sources of different temperatures. So I've switched to using a gray card and find it works much better.

working on it in Middle TN
Nikon D3100
18-55 mm Nikkor VR
55-200 mm Nikkor VR
55-300 mm Nikkor VR
150-500 mm Sigma OS

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