This is an interesting video. I wonder if he had some training of some sort.
I used to teach that exact sweep, even to stepping into it, but the target was the opponents arm. You grabbed the wrist with your right hand, turned it clockwise, thereby turning the opponent away from you. The left hand came up and buckled the opponents elbow ending with them restrained with their hand behind their back in a pain hold. It was quite effective.
These were defense for healthcare provider classes so I'd be surprised if it was unique to them, but he did exactly as I would have taught it, except he got a gun instead of an arm.
It was our favorite move, it would let some 98lb nurse make some pretty hefty guys look silly if you were fast enough.
