WB is done by amplifying the red and blue channels (while usually leaving the green unchanged) with multipliers that are appropriate for a given light temperature. For instance, the WB for daylight might be something like R X 2.0 and B X 1.4; because daylight is blue, the red channel has to be boosted more to compensate for it. The exact choice of multipliers is also influenced by the Nikon profile that the camera uses when making a jpg, because it determines how the red and blue channels are rendered before balancing. But when making a Raw file no WBing is done by the camera to the Raw, although the multipliers are listed in the metadata. LR reads those multipliers and uses them when "As Shot" is set. But the LR GUI does not show multiplier values (which could be confusing for some users). Instead it shows the temperature of the light that could have required the use of those specific multipliers. IOW, the camera does a calculation from the temperature to the multipliers while LR does the reverse calculation from multipliers to temperature. It reaches a different result because of two factors; A.) color temperatures do not refer to a single color, but rather a range of colors, and B.) LR's processing does not use the Nikon-made camera profile, but rather its own Adobe-made profile,which is inevitably different. Bottom line - the temperature reading on the LR GUI is a "sort of" thing that should not be taken too seriously. The important thing is that greys that should be neutral are in fact neutral.
Thank you for your explanation - I now understand the difference between the camera and LR.