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It's obviously impossible to tell whether the rider came from the track or not, as the clip starts with him in a position that could indicate either, but it's actually not permitted to turn left from the track there. For this to be possible, there would have to be a 'jug handle', i.e. a spur from the track that can release riders into the main carriageway. The track crossing itself is only for people to cross to the other side of the track, and no other manoeuvres. The rider is in the wrong in any case (quite apart from the headbutt). (I don't blame him if he didn't know that you can't turn left there. Almost nobody does.) I also don't blame pedestrians for wanting to cross parallel to the cycle crossing.
It's not a pedestrian crossing, it's where the cycleway crosses the junction. There is no green light for pedestrians there. If the rider came from the cycleway he had a green light. City of London police are making claims that aren't true, or at least can't be shown from their edited clip.