Could it be the only reason they backed off was because they saw the approaching police vehicle?
Whatever the case I get this all the time when on a bicycle. Some people don't treat cyclists as equals, don't give them sufficient room, and assume cyclists should "ride in the gutter" at all times. All of which can easily get a cyclist killed.
I always say if in doubt, ask yourself if you'd do the same to a car. Then add extra space on account of the vulnerability associated with cycling. Unfortunately many people seem only too eager to forget this and it causes problems.
I also think the cyclist should take primary earlier on, where possible, and filter on the right. Filtering on the left especially at that speed is incredibly dangerous (pedestrians darting between stationary traffic and people exiting vehicles without checking). The cyclist also pulled up on the motorcyclist with little to no warning, just as the lights were about to change.. a motorcyclist who was turning left. I would have at least waited behind the motorcyclist.
Looks to me like the instructor was telling the learner driver to drive defensively - and rightly so. Idiots like the one behind them are the reason people die.
And thank you for sharing this. Hopefully the idiot will learn from it and stop being an anti-social asshole.