Agreed - the sample size is also really small to be interpreting slower arrival times as well, if only 1 or 2 packages took a long time it's likely they just found an outlier.
In the original article, one of the footnotes mentioned that they tested the data using Wilcoxon's Signed-Rank test, which mitigates a lot of the impact of single outliers.
I'd love to see the raw data though, to see an even less-sensitive method to outliers (sign test). If the difference between the groups is as large as the article would lead us to believe, the loss of power should not present any problem.