From the comments on this two-year-old article:
With respect to "proper OCD adjustment", we followed all guidelines provided with the equipment at the time (it is our understanding that certain aspects about the OCD's use have been changed/elaborated on since this experiment).
In other words, how they used the tool was not how the tool was designed to be used, but they didn't know that they weren't using it properly at the time. This was not their fault; I thought that how to use the OCD as intended wasn't clear until Sasa released his OCD v2 usage video. I know that I was using mine incorrectly.
For example, the coffee is to be levelled in the basket, e.g., with Stockfleth's or WDT, before using OCD. Socratic didn't do this, so one could suspect that the coffee piled in the center of the basket to be compressed more than coffee at the edges. That would be my guess as to "Why would a distribution tool reduce TDS?" This could also explain why they found that the interaction between type of grinder and OCD was significant. In addition, depth of the OCD has to be set carefully - as Sasa says, the OCD is not a tamper; its usage should not compress the coffee.