You probably already know this, but once you've passed an image through Camera Raw, image settings are saved per-image.
Also, the Camera Raw Defaults are saved separately per-camera.
Is it possible you opened that image before, possibly in a group, and set the White Balance values manually?
If not, are you sure you don't have a custom white balance specifically set at 4800K saved in the Camera Raw Defaults for your D80? These are completely separate from the settings for your D90.
1. Open a D80 raw image.
2. Click the fly-out menu button, and choose Camera Raw Defaults.
3. Is the White Balance still showing Custom?
4. If so, change the White Balance to As Shot.
5. Click the fly-out menu button, then choose Save New Camera Raw Defaults.
6. Now shoot a new test image with the D80, and open it.
7. What's showing for White Balance?
Yeah, that's the only answer. And here is where I got snookered.
I have both cameras set to 4800. But the D80 actually does not set 4800. It sets 4700; Tint-2. The D90 sets 4800: Tint -4 So, some years back, I set ACR for the D80 to Custom and manually set 4800K;Tint -4... and forgot about it! Why I didn't catch it on this batch is that the colors were so far off. The difference between 4700 and 4800 isn't big and if all I had was the D80, I would have left it there. But shooting the same with both cameras, correcting the D80 to actually exhibit the same WB as the D90 became prudent. For one thing, we would have arguments over the differences between the D90 and the D80 (which is the "right" color). My SO is a colorist and while I can see subtle differences (and maybe not as sharply as she does) I don't fret much over that. Well, maybe more than I used to. She is a good teacher about color!.
It POed me when I first saw that 4700 figure from the D80. In it's menu, the option is 4800, not 4700, dammit! But I knew I would be tweaking it in ACR if necessary using the WB dropper.
So now I have some decisions to make. Much of the output, in fact, all of it until her last session is set to that 4800 by using custom. Now I am sure she will want to use auto, that is until she sees that it will eventually work against her, even using the Nikon View NX on her computer. I think I can use Preset for making two choices available; Custom 4800 or As Shot, but I don't know for sure.
I gotta go make some coffee. 6:30 comming up and I haven't had any!
FWIW, I went back to my Custom settings for the D80 at 4800K as before, and configured As Shot with all settings other than WB to be the same Custom. Therefore, switching back and forth assures only showing the WB change. Basically, back to where I was except now I know not to mess with things before coffee! Forgetting coffee is hazardous to running your PS.
Happy to help.
One of Photoshop's greatest strengths and weaknesses simultaneously is its modality. You can set it up to be a personalized, hugely-powerful engine just to get what you want done, and quickly, but at the same time that modality can be absolutely maddening if you don't keep on top of it.
...and always keep in mind when suddenly things don't seem to be working any more:
That's what I did, and I discovered my error by actually openeing a file which I knew did have the WB set manually on the D80, and discovered it was opening as Custom. I assumed it was opening as "As Shot".