No his argument is that there are two sampling biases. The demographics of a tested population do not match the demographics of the county. If someone believe

No his argument is that there are two sampling biases. The demographics of a tested population do not match the demographics of the county. If someone believes they've been infected they are more likely to seek testing. (self-selection bias) The study adjusted for the first but not the second bias. He believes the second bias is more important, so when they adjusted for the first they moved the adjusted average farther away from the true average. I think he's right, self-selection can be a far more impactful bias than things like sex and race.