Yes, legally speaking it is. You appear to disagree, we shall have to agree to differ.
I think that it was utterly unneceserry for the police to stop this man, let alone speak to him in a rude and aggressive manner.
I thought it was utterly unnecessary for the cyclist to do what he did instead of remain at the light until it changed like the other cyclist did who was beside him at the line.
Cyclist definitely says "green man". He might have been making that up but, either way, he is comfortably across and on his way before any other traffic moves. I reckon he knew perfectly well from experience that he had time to do it. It doesn't mean that he is not a cock of course but all this rationalising it as a crime is just nonsense.
I don't think it has been rationalised as a a crime as I think we have established that no offence has been committed by UK law but what I am saying that in my opinion what he did was irresponsible and unnecessary so therefore on that reasoning the Police officer was right to speak to him, I don't think he was overly rude or aggressive in the circumstances. I can imagine that as he was stopped in the road, he was expecting it to be a quick word and on you go but the cyclist then began arguing.
If it was me in the circumstances and I was stopped I would accept what was being said and research it myself or gauge opinion with my peers later on what was not only legal but what was usual cycling etiquette for future not start arguing with the officer at the roadside. I was brought up to respect the Police and wouldn't identify that as harassing me.
The example I could give is that when cycling I signal when turning to inform other road users of my intentions, I know other cyclists who don't, plenty of car drivers don't. I am unlikely to be prosecuted if I don't but think its the right thing to do and is in the highway code. If a Police Officer stopped me if I didn't signal to inform me that I should I wouldn't get on the offensive and say "But I don't have to".