You are in a built-up area. Have you acted accordingly by allowing the bus driver to merge into traffic?

In a built-up area, a driver is required to reduce speed, and if necessary stop, to allow a bus to join the traffic from a marked bus stop. In the situation shown in the video, the bus driver is clearly signalling their intention to pull out from the bus bay, therefore allowing them to complete this manoeuvre is the correct and legally required action.