What you don't see in the video is that Roger Phillips is moving in a way to bring threats behind him (or otherwise outside his field of vision) into focus. The reason for this is very clearly illustrated in this document from Safeism– read the whole thing (It's short and to the point) but I am referring to the last section- starting on page 11.
By using all the techniques described in this document together you are able to quickly assess not only the threat in front of you, but also survey for additional threats with without losing sight of the threat in view (unknown contact). Keeping distance using the fence technique is key- and using all these techniques allows you to assess your options for fight or flight. Even if you're not armed this technique can buy you that extra step to escape and help avoid running into a potential ambush outside your vision.