Those Farage-saluting farmers literally blocking roads with their tractors? Cheered on as the “Farmy Army” by the press. It’s completely different, isn’t it and, of course, tractors can’t cause accidents and never stop ambulances from passing.

No, no they couldn't have. Pedestrians literally legally cannot cause an accident with a vehicle. The driver will always be liable, even if those pedestrians are breaking the law.

Pearl-clutching is unbecoming of you, cut it out.

how exactly could they have caused a serious accident? violently slamming their bodies against a car with such force that it crumples the front?

There is a sense in which they are related though, and that's that they're both things that fall under the justice system. I understood the person you're replying to as making a general point about their lack of faith in the justice system by juxtaposing a case with disproportionate punishment with a morally awful but unpunished case. The two examples aren't directly related, but that's why the contrast works — it's two facets of a fucked up justice system.