This was a Critical Mass event, which is why the bicyclists are taking up all of the street as a way to reclaim the streets and protest the lack of safety for riders under usual conditions. It’s not legal, but protests are never useful if they’re fully legal now, are they.
Idk about the usa but here in europe its EXPLICITLY written into the drivers code that even if someone is driving illegaly if its in your power to stop an accident you have to. So if a person steps in front of you randomly and you have half a second to react thats usually not your fault BUT if you for example saw that there was a school bus dropping kids off and then you hit a child running across the road theres a large chance that theyre gonna charge you. Of course in europe you have to put like 30 hours into theory and then a lot of driving lessons to get a license while in the usa you basically get a drivers license instantly and nobody gives a fuck so thats why people dont know the rules…
The US license comes with the troop loops.
To add, in the Netherlands, known for it’s stellar bike infrastructure it’s exactly with actions like this that they reclaimed their cities from being purely car oriented.