It's physics:
The lower your center of gravity, the easier it is to quickly change direction. He's an ankle-breaking machine.
It's optics:
The shorter you are behind behemoths, the harder it is to track your location.
This kid's not breaking anything but arm tackles. But often, that's all defenders will be able to offer.
One vital requirement for his success: he'll never do squat on plays where the line doesn't offer some daylight. You can run him inside or outside, but if they can't give him a window, it's gonna be ugly.