I read it yesterday and thought about it a bit, looked at it again today. A few thoughts as follows:

There are basically three kinds of resistance a touring cyclist has to push against, (1) aerodynamic, (2) rolling friction, (3) and elevation change. Aerodynamics, from the photo he is riding on the hoods which is not the most aerodynamic position, but is likely more aero that a flat bar rider would use. Thus, it appears to be pretty comparable to most touring riders. Rolling friction on his bike is probably similar to most other touring bikes, he used a LHT and from the photos it looks like his tires are between 32 and 37 mm (this is my guess). In this case, elevation change is essentially non-existent. So, in this regard his test is quite similar to the typical bike tourist.

But there is a big difference in power and speed. I have been part of a few group tours and I usually was near the median or slightly faster than median for speed. Thus, I think my speed is about typical or slightly faster. In the winter most of my cardio exercise is on an exercycle at a health club and from that I know that my wattage is in the 120 to 135 watt range on the exercycle which has a wattage readout. I am pretty sure that the exercycle wattage is about right, but for brevity I will skip explaining why. I know that the exercycle wattage would be comparable to my touring wattage because I use a heart rate monitor, thus I know that my heart rate at the health club is about the same as on a touring bike. And I think my average rolling speed while touring is somewhere between 11 and 13 mph on pavement with 37mm tires, that speed range largely depends on hills and headwinds. Reduce about 1 mph for a good quality rail to trails type of hard packed trail with a wider lower pressure tire.

But the test was done at 200 watts, which is roughly 50 to 70 percent more wattage than I exert. That also shows up in his speed that averaged 27.78 to 30.17 km/hour, or 17.26 mph to 18.75 mph. Even on my best day, I would not be even close to pushing that kind of speed on a touring bike with a load for any significant distance without some help from a tailwind.

I do not have any expertise in the science of aerodynamics, but I think at lower speeds aerodynamics is less critical and rolling friction becomes a bigger factor. Thus, I am not sure if you can really say that front and rear panniers would be 7.9 percent slower than bikepacking gear when a slower (and I suspect more typical) rider uses that gear on their bike. It would have been an interesting comparison if it was done at a more typical touring speed.