Always a place for cynicism for sure. IMO they are trying to they are trying to compare the ATS to a simple control (tank with no filtration) . The next step could be skimmer to control. Which will give a degree of comparison. After that they could put them head to head. One challenge for the skimmer group is all the variables - water height, air and water flow. ATS has a few variables as well - light spectrum, intensity and contact time ( water flow rate) .
My cynical guess is that the skimmer tank (alone) removed significantly less phosphates/nitrates than the ATS tank (alone) removed, so a skimmer tank (alone) wasn't included in the data because it'd make the skimmer look bad, and skimmers are money makers.