At 33 seconds (
http://www.bbc.co.uk/news/uk-17069235 ) the bus is moving from its bus lane onto the roundabout (check out the Google map satellite image of the junction), is indicating right, and is in the process of changing lane.
The cyclist at that point is in primary position, behind the bus on lane to the right,with a clear view of the direction of travel of the bus and of the rear right indicator.
The cyclist had a choice: Keep line and speed and end up along side the bus sharing the lane OR slow slightly and slot in behind the bus. He chose the first option.
Look at that portion of the video without knowledge of the subsequent events.