The price per ton of Chardonnay is relatively inexpensive, especially if you're getting your grapes from outside of Napa. Also, by California law only 75% of the grapes have to come from the named varietal on the bottle, so they could easily be blending in some Chenin Blanc or Sauvignon Blanc for consistency. Lastly, there is a lot of post-production stuff you can do to Chardonnay, most famously involving oak, but there is other stuff as well. So it seems possible that they can source from a wide variety of vinyards and still have a relatively consistent product, given the wide variety of options available under California law.

If that's true, then it's a serious flaw in the methodology of the people who do the testing. They shouldn't allow the brewer to submit the samples. They should pick a few bottles of the same vintage from various retailers and mix them together.