I dont understand what you said at 19:06 about why Face Snapping wouldn't work. Would you mind explaining?
Too long for a reply but I might have an idea what he meant.
He stated it wouldn't work without a secondary object.
Which I believe is due to since he deleted that part of the face prior you would need the removed mesh potion there to actually face snap to.
Also it might of required us to do it vertex by vertex which may result in a slightly less correct circle-ish shape.