The authors made various claims or implications not backed up by their experiment.
However, it absolutely does not answer the question that is asked in the title of the paper, and the process they use is incapable of answering that question.
If you go back and read the original CIFAR10 paper, you'll see that the process they carefully went through meant that they curated the most suitable images for each category. By definition, what's left over (which is what the Recht et al paper chose from) is less good images, which are of course therefore harder to classify.
All the experiment measures is how good they are at matching the distribution of the original dataset. The answer, they discovered, is: not very.
However, it absolutely does not answer the question that is asked in the title of the paper, and the process they use is incapable of answering that question.
If you go back and read the original CIFAR10 paper, you'll see that the process they carefully went through meant that they curated the most suitable images for each category. By definition, what's left over (which is what the Recht et al paper chose from) is less good images, which are of course therefore harder to classify.
All the experiment measures is how good they are at matching the distribution of the original dataset. The answer, they discovered, is: not very.