Hybrids use generators rather than ICE. As such, they are more efficient burners of gasoline, reducing pollution per mile.
The study said that they're better: 19% better. That's not nothing! It's just not the 75% better that lab testing showed.
The link you provided is the experience of one driver, one who is conscientious and focused on minimizing fuel consumption (within reason; hypermilers would do better). The study looked at the real-world results across 800,000 drivers, most of whom apparently didn't take so much care to minimize fuel usage.
Also, it's not true in general that "hybrids use generators rather than ICE". That's true of PHEVs that are strictly serial hybrids, but most are series-parallel or "power split" hybrids, meaning they can drive the wheels with the electric motor, or the combustion engine, or both. Often both the electric motor and the ICE are too small to provide the target maximum performance so must be used in parallel when you step hard on the accelerator.
One fascinating strategy for power splitting is "through the road", which has no mechanical connection at all between the ICE and the traction motor, and uses the wheel-driven traction motor as the generator. The way it works is the ICE drives one axle and the traction motor drives the other. Battery charging is done "through the road", using the road itself to transmit power from the ICE-driven axle to the electrically-driven axle. The ICE spins one pair of wheels, driving the vehicle forward, which forces the other pair of wheels to spin which turns the electric motor which charges the battery. This only makes sense in AWD drive cars but it's peak design elegance.