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.
The OP has some context but Lemmy is bad about showing the text included with a media post so it’s easy to miss. The OP states it’s a “critical mass” protest where large numbers of cyclists reclaim the street to demand better bicycle infrastructure
I figured that was happening, which is why I updated the title to explicitly state it’s a Critical Mass event