The difference is that Trailer Life's tests were done with an EMPTY truck with only a 150lb driver. No passengers. No stuff. No dog. No bicycles. No firewood.
Normal people have all that stuff in the truck, adding hundreds of pounds to the truck and taking away hundreds of pounds worth of tongue weight carrying capability.
In this test, most of the truck's payload capacity was taken up by the 9000lb trailer's tongue. At 12%, the tongue is 1080lbs, and that's being optimistic. 9000lb trailers tend to have much heavier tongue weights than that.