The cyclist (and motorcyclist) is following the rules. Rules designed to put them in less danger than sitting in traffic.

Here’s rule 88 of the Highway code, which simply assumes you’re going to filter because it is safer to filter (and your motorcycle instructor will have told you to filter, and your test examiner will fail you if you do not filter).

Rule 88

Manoeuvring. You should be aware of what is behind and to the sides before manoeuvring. Look behind you; use mirrors if they are fitted. When in traffic queues look out for pedestrians crossing between vehicles and vehicles emerging from junctions or changing lanes. Position yourself so that drivers in front can see you in their mirrors. Additionally, when filtering in slow-moving traffic, take care and keep your speed low.