but there there might be more to it
The bus driver should have made sure that he could overtake safely before attempting to do so, which he clearly failed to do.
But this is the UK, and the law does say that the cyclist should not do anything to hinder a vehicle that is overtaking, so the cyclist should have let the bus complete the overtake without riding back up alongside and banging on the windows, once the bus was in front it had the right to use its brakes.
It is not entirely clear from the video if the bus did get fully in front, I think it probably did, the camera lens is not particularly wide angle, so makes it look like the cyclist is further forward than reality when viewed by people used to dashcam video, it certainly got its rear wheels well passed the cyclist, and at that point the cyclist should have accepted that the bus was going to pull back in and it did not make sense to argue about the last few mm.
It is clear that this is a cyclist who owns the road and will stop for nobody, not even the red traffic light he flew through at the start of the video, where the other bike had stopped. This is definitely not a good example of how to ride a bicycle under UK traffic laws, and if he had been injured and tried to take the bus driver to court, the court would put a significant amount of the blame on the cyclist.