Is there a reason that guy is straddling two lanes, or is he just a dumbass?
I used to ride like that ('70s, '80s and maybe '90s too). I was taught and encouraged to occupy the nearside of any lane I was riding in.
That was the consensus in those days. I was taught to do so at Cycling Proficiency. In a road system like the one in the vid, that often translates into riding on or right alongside the lines between lanes.
On a roundabout or in a multi-lane system (my school ride took me over Blackfriars Bridge) I would ride on the left of any lane I wanted to follow - and filter as appropriate. I translated this method into extra-urban riding, where motor traffic was often moving far faster than me.
It was a long time (decades) before it dawned that I was moving much faster than I had earlier and that I might make my progress a little surer and safer if I moved right a little in some circumstances. Riders who ride like
White Line Johnny in the vid are not necessarily dumb-asses; they may be doing what they were taught to do and have not yet felt the reason to change.
I did change, but I still use 'primary' a good deal less than many other riders I see in traffic.