What might cause this discrepancy?
You haven’t given any clues as to what the data really relate to (e.g., what sort of sales) and why you have been asked.
Looking at the above responses… You should be asking (or already know) how the samples were obtained for the two groups, check your calculations, understand the data beyond those median calculations…
Did you receive any other data apart from lots of discount percentages? If not, ask why they want you to do such a trivial calculation. Compare the additional data between the two groups to look for explanations. Ideas: are the bigger discounts linked to seasonal demand, more experienced sales personnel, bulk purchases.
Additionally, just comparing the medians will not be interpretable. Essentially you’ll be comparing 1 data point from each group [precisely so if you have an odd number of data per group], but what about the other data? You’ll get a better idea of the entirety of the discounts if you also consider some/all of minimum and maximum, interquartile ranges, mean and SD…