Since, line 16 code D of 1120-S Schedule K-1, is for distributions, I would say they either made a mistake or there is something they consider a distribution that you are unaware of.
There could be items the business spent money on that was determined did not qualify as a deduction. These non deductible expenses are divided among the owners as distributions. A common non deductible expense is 50% of meals and entertainment.
For example, if the S-corp recorded expenses for meals and entertainments (which is only 50% deductible), the other half is considered a "distribution" split amount the owners by ownership percentage.
You are entitled to an answer as an owner. You can try calling them if you don't think they made a mistake.
