Interesting scene here, not one we've noticed before.
This the Cotham Hill/St Michaels Hill mini roundabout, one of the high points of the city, and wonderfully representative. This is an excellent example of how the removal of traffic lights permits an efficient traffic flow.
But today, cars aren't exiting Cotham Hill. At 0:10 you can see why. The parent on the school run has opted not to pull over into the cycle lane, or even drive to keep-clear area in front of the school. Instead they just stop at the top of the road, let the kid out, a child who can then safely walk to the traffic island, and then over one more lane before reaching a zebra crossing, then get to school. The parent can get to their destination without any detour, without even struggling to get their car out of the bike lane and into the main car lane.
This action encourages physical activity in the child, and reduces congestion near the school. It also enable the child to cross the road safely. At 0:18-0:20 you can hear one of the vehicles behind expressing their concerns over this action, by sounding the horn. But if they were on the school run, why not let their kid out at the same time?