Seriously flawed article.
They compare Gladiator sales against the F150 and Tundra full size trucks then later compare the size to the Colorado and Tacoma. On paper, the Gladiator is a competitor to the Colorado, Ranger, and Tacoma but is more of a premium lifestyle vehicle. The sales price reflects that. As a result, the light pickup crowd will not seek out the more expensive Gladiator. Instead, they will search for more conventional and cost effective vehicles.
I have no idea what the sales goals were for the Gladiator. Knowing it's targeted at a specific market segment and is priced far more than the average midsize truck, I can't imagine Jeep expected to hit 100,000 units per year.