Just an observation:
The presenter in the vid is drilling using distancing to defend himself, not using one arm. If he dropped that one arm by his side, his attacker would be swishing though air.
When I'm feeling cocky, I'll sometimes spar with one hand to try to and cross my partner up and pin both of his arms with one of mine, or flank him on the outside so that I can disrupt his balance with one arm. But to do either I'll have to end up right up close and personal with him.