I just heard it directly from the horse's mouth. It was user error.
Apparently the car was tight, so he kept pushing the wing forward. By the geometry of the wing slider, the wing gets less and less angle the farther forward you push it. Ideally, you want to set the angle for where the wing will probably be, and make minor adjustments from there. According to out driver, the wing was almost level when he lapped Randy, and shaking a little up and down.
And then he moved it forward another two inches. That caused the wing to make lift instead of downforce, and luckily the wing shredded instead of pulling the car off the ground. Almost exactly the situation that I described to Jammer earlier.
I don't think you'll find much on YouTube about that, since it's usually very rare. Cars flipping (on dirt) are a LOT more common.