Why would that one sharpener cause a knife to dull so badly? He used the same model of knife for all testing. New, dull it, sharpen it, test sharpness, hardwood, test sharpness. I couldn't tell if he only used one knife per sharpener (sample size = 1). If so, I tend to wonder if he had a bad blade.
Probably he created a fairly large burr and didn't remove it. A wire edge will seem pretty sharp but the work-hardened metal will quickly fail. That's why deburring is such an important step but one he ignored. I usually use a leather belt on my grinder because it works quickly and I'm lazy.
But a leather strop, hard felt, some cork or balsa wood or even the end grain of a block of wood will do the job. You need to try not to create a huge burr; that makes removing it easier.