Why is it meaningless? It is still interesting and important to look for fraud during a single, particular election. Especially, one could argue, in the most recent one, since that presumably means bad-actors are more likely to be active in the next presidental election. I agree that it is interesting to see if voting fraud is common or widespread in primary elections in general, but studying individual events is not useless.
It occurred to me that you may have meant to say that the analysis is not robust without historical comparisons to establish that such anomalies are not just statistical fluctuations? That would something worthwhile to explore. It seemed (from very quickly skimming the pdf) that they did try various statistical tests to ensure their results were robust. But comparison with other datasets would likely provide a good test of the robustness of their findings.