Like Noah, after reading the stimulus, I immediately pre-phrased representativeness of the sample (although now I understand that the argument doesn't assume representative sample).
I approached this question as a #/% flaw and because the argument is comparing proportions/percentages based on two different groups (Sample vs entire manufacture), the idea of representativeness really struck me and I believe this is what the LSAC aimed to exploit in order to trap test takers. But isn't the representativeness is one of the necessary qualities for a valid sample?